Giving the geological ages, rock systems, strata and the development of
life, with their relative positions and order of succession, according
to the latest scientific knowledge. Many attempts have been made to
compute from geological, physical, and other data the length of the
period during which the earth has been in a solid state.
Geologists, however, are disinclined to accept any period much less than
100,000,000 years as sufficient for the elaboration of the present
structure of the earth. It is indisputable that many millions of years,
probably thirty or forty, must have elapsed while the great sedimentary
rocks were being deposited. With respect to the larger features of the
earth’s surface, it is likely that two different kinds of movement are
responsible. Where the contraction of the earth has caused a lessening
of the support below the surface, there has been a subsidence of great
areas. In the second place, where the rigid crust has been able to
contract into a smaller space, great mountain ridges and folds have been
formed. The subsidences which caused the ocean took place at different
ages. The Atlantic Ocean probably dates from middle Cenozoic times; the
Indian Ocean may be older; the Pacific suffered great modifications in
comparatively recent times.
+-------------+------------------+------------------+-------------------+
|=Life Ages | =Rock Systems= | =Series of | =Characteristic |
|of the Earth=| | Rock Strata= | Rocks= |
+-------------+------------------+------------------+-------------------+
| | |Recent, or Human. |Alluvium, sand, |
| | | |gravel, mud, clay, |
| | | |marl, loess. |
| | | | |
| | |=Pleistocene= |Drift, boulder |
| | |(_plīs´tŏ-sēn_), |clay, gravel, |
| |=Quaternary= |or “most recent.” |loess, silt, gla- |
| |(_kwa-ter´na-ri_) |Glacial Period. |cial deposits and |
| |or “fourth.” Once | |other formations |
| |supposed to be the| |formed during |
| |_fourth_ sedimen- | |glacial period. |
| |tary system. Age | | |
| |of man. |=Pliocene= |In East and West, |
| | |(_plī´ō-sēn_), or |land deposits pre- |
| | |“more recent.” |dominate. Marine |
| | | |sands, clays, marls|
| | | |on Atlantic and |
| | | |Pacific coasts. |
| | | |Igneous rocks in |
| | | |West. |
| +------------------+------------------+-------------------+
| | |=Miocene= (_mī´ō- |On Atlantic coast: |
|=Cenozoic= | |sēn_), or “less |sand, clay, shell |
|(_se´nō-zō´- | |recent.” |marl, diatomaceous |
|ik_), or | | |earth. In West: |
|“Recent | | |sandstone, shale, |
|life.” | | |and diatomaceous |
| | | |material. Extensive|
|_Estimated | | |volcanic formations|
|Age of | | |in Rocky Mountains |
|Period_, | | |and Great Basin |
|=3,000,000= | | |region. |
|_years_. | | | |
| | |=Oligocene= |Limestone in |
| | |(_ŏl´ĕ-gō-sēn_), |Caribbean region, |
| |=Tertiary= (_ter´-|or “a little more |and deposits in |
| |shi-a-ri_), or |recent.” |West. Marine and |
| |“third”. Once | |fresh water beds on|
| |supposed to be the| |west coast. Many |
| |_third_ sedimen- | |coal beds in Puget |
| |tary system, or | |Sound. |
| |Age of mammals. | | |
| | |=Eocene= (_ē´-ō- |In Eastern States: |
| | |sēn_), or “dawn of|clays, sands, |
| | |recent.” |greensand marls. |
| | | |In West: conglom- |
| | | |erate, sandstone, |
| | | |shale, diatomaceous|
| | | |shale and igneous |
| | | |formations are de- |
| | | |veloped. Many coal |
| | | |beds in Puget |
| | | |Sound. Fresh water |
| | | |beds in western |
| | | |interior. |
+-------------+------------------+------------------+-------------------+
| | |{Upper. |In East: sand, |
| | |{ |clay, and greensand|
| | |{ |marl. In West: |
| | |{ |sandstone, shale, |
| | |{ |limestone, chalk, |
| | |{ |extensive coal |
| |=Cretaceous= |{ |beds, various |
| |(_krē-ta´-she-us_)|{ |igneous rocks. |
| |or “bearing |{ | |
| |chalk.” |{Lower. |Clay, sand, gravel |
| | |{ |on Atlantic coast |
| | |{ |and Gulf. Sedi- |
| | |{ |mentary and igneous|
| | |{ |rocks on west |
|=Mesozoic= | |{ |coast. Some non- |
|(_mĕs-ō-zō´- | |{ |marine beds in |
|ic_), or | |{ |Texas. |
|“Middle +------------------+------------------+-------------------+
|life.” | |{Upper. |Probably not repre-|
| |=Jurassic= (_jȯȯ- |{ |sented in East. |
|_Estimated |ras´sik_), or like|{ |Sandstones, lime- |
|Age of |the mass of the |{Middle. |stones and shales |
|Period_, |Jura Mountains. |{ |in West. Some “red |
|=9,000,000= |Age of Reptiles. |{ |beds” in western |
|_years_. | |{Lower. |interior. |
| | | | |
| | |{Upper. |In East sediments |
| | |{ |formed in shallow |
| | |{ |troughs between re-|
| | |{ |cently formed moun-|
| |=Triassic= |{ |tains. Considerable|
| |(_trĭăs´ĭk_), or |{ |bodies of igneous |
| |in a triple |{Middle. |rock, traps, and |
| |series. |{ |other flows and |
| | |{ |dikes. “Red beds” |
| | |{ |in West with salt |
| | |{ |and gypsum. Some |
| | |{ |igneous rocks on |
| | |{Lower. |west coast. |
+-------------+------------------+------------------+-------------------+
| | |=Permian= (_per´- |In East fresh water|
| | |mē-ăn_), like |sediments including|
| | |those at Perm, |coal; in West “red |
| | |Russia. |beds” probably of |
| | | |continental origin.|
| | | |Some marine sedi- |
| | | |ments; salt and |
| | | |gypsum in red beds |
| | | |in Kansas. |
| | | | |
| |=Carboniferous= |=Pennsylvanian=, |In Eastern States |
| |(_kăr-bŏn-if´-er- |like those of |grits, sandstones, |
| |us_), or coal- |Pennsylvania. |shales, limestone |
| |bearing. Age of | |and coal. In |
| |Amphibians. | |Western States much|
| | | |limestone; no coal.|
| | | |Igneous rocks on |
| | | |west coast. |
| | | | |
| | |=Mississippian=, |Limestones pre- |
| | |or Lower Carboni- |dominate with sand-|
| | |ferous. |stones near base |
| | | |and shales near top|
| | | |of series. Igneous |
| | | |rocks in |
| | | |California. |
| +------------------+------------------+-------------------+
| |=Devonian= (_de- |{Upper. |Sedimentary rocks, |
|=Paleozoic= |vō´ni-an_) like |{ |limestones, sand- |
|(_pāl-æ-ô- |those of Devon- |{Middle. |stones, shales; |
|zō´ic_), or |shire, England. |{ |igneous rocks in |
|“Old life.” |Age of Fishes. |{Lower. |Maine, Nova Scotia,|
| | |{ |and New Brunswick. |
|_Estimated +------------------+------------------+-------------------+
|Age of | |{ |Sedimentary rocks |
|Period_, | |{=Ontarian= (_on- |predominate; con- |
|=24,000,000= |=Silurian= (_si- |{tā´rē-ăn_), place|glomerates, sand- |
|_years_. |lū´ri-an_), in the|{name. |stones, shales, |
| |land of the |{ |limestones, salt, |
| |Silures, England. |{=Champlainian= |gypsum. Igneous |
| |Age of In- |{(_shăm-plān´ē- |rocks in Nova |
| |vertebrates. |{ăn_), place name.|Scotia, New Bruns- |
| | |{ |wick, and Maine. |
| +------------------+------------------+-------------------+
| | |{=Cincinnatian= |Chiefly limestone |
| |=Ordovician= (_ŏr-|{(_sĭn-sĭn-năt´-ē-|with subordinate |
| |dŏ-vīsh´ăn_), a |{ăn_), place name.|sandstone and |
| |place name in | |shale. Rocks great-|
| |Wales. |{=Mohawkian= (_mō-|ly folded in New |
| | |{hŏk´ē-ăn_), place|York, in Taconic |
| | |{name. |Mountain region. |
| +------------------+------------------+-------------------+
| | |{ |Mainly sandstones |
| | |{=Saratogan= |with some shales, |
| | |{(_săr-ă-tō´găn_),|and in Western |
| | |{place name. |States considerable|
| |=Cambrian= (_kam´-|{ |limestone. At some |
| |bri-an_), from |{=Acadian= (_ä- |places rocks are |
| |Cambria, the old |{kād´ē-ăn_), place|changed by pres- |
| |name for Wales. |{name. |sure, especially in|
| | |{ |the Appalachian |
| | |{=Georgian= (_jōr´|Mountains. Upper |
| | |{gē-ăn_), place |Cambrian covered |
| | |{name. |larger area than |
| | |{ |lower Cambrian. |
+-------------+------------------+------------------+-------------------+
| | |{=Keweenawan=, |A great series of |
| | |{(_kē´wē-năh- |sandstones, lime- |
| | |{wān_), pertaining|stones and shales, |
| | |{to Keweenaw Pen- |in middle portion |
| | |{insula, Michigan.|of which are many |
|=Proterozoic=| |{ |enormous flows of |
|(_prō-ter-ō- | |{ |lava. |
|zō´ik_) or |=Algonkian= (_ăl- |{ | |
|“Former |gŏn´kē-ăn_), from |{=Huronian= (_hu- |Three great series |
|life.” |district of |{rō´nē-ăn_), |of sedimentary |
| |Algonquin |{rocks on borders |rocks, sandstone, |
|_Estimated |Indians, north of |{of Lake Huron. |shale and lime- |
|Age of |St. Lawrence. |{ |stone, and iron |
|Period_, | |{ |formation. Contains|
|=18,000,000= | |{ |also many great |
|_years_. | |{ |igneous bodies, |
| | |{ |acidic and basic. |
| | |{ |Lower members much |
| | |{ |metamorphosed by |
| | |{ |pressure. |
+-------------+------------------+------------------+-------------------+
| | |{=Laurentian= |Granitic rocks and |
| | |{(_law-ren´shi- |gneisses that are |
| | |{an_), pertaining |believed to be |
| | |{to rocks along |granitic rocks |
| | |{the St. Lawrence |metamorphosed by |
| | |{River. |pressure. Formerly |
| | |{ |supposed to be |
| | |{ |older than Keewatin|
|=Archaeozoic=| |{ |and regarded as the|
|(_ar´kē-o-zō´| |{ |“original crust of |
|ic_), “With- | |{ |the earth.” |
|out life.” |=Archean= (_är- |{ | |
| |kē´-ăn_), |{=Keewatin= (_kē- |A great schist |
|_Estimated |“oldest.” |{wā´tĭn_), rocks |series made up of |
|Age of | |{in a district of |lava flows, tuffs, |
|Period_, | |{Manitoba, Canada.|and volcanic ashes.|
|=18,000,000= | |{ |With these are sub-|
|_years_. | |{ |ordinate sedimenta-|
| | |{ |ry rocks; sand- |
| | |{ |stone, shale, lime-|
| | |{ |stone, and iron ore|
| | |{ |formations nearly |
| | |{ |everywhere greatly |
| | |{ |metamorphosed by |
| | |{ |pressure. Includes |
| | |{ |the oldest rocks |
| | |{ |known. |
+-------------+------------------+------------------+-------------------+
+-------------+------------------+------------------+-------------------+
|=Life Ages | =Rock Systems= | =Series of | =Forms of Life= |
|of the Earth=| | Rock Strata= | |
+-------------+------------------+------------------+-------------------+
| | |Recent, or Human. |Man predominant. |
| | | | |
| | |=Pleistocene= |Mammoth, mastodon, |
| | |(_plīs´tŏ-sēn_), |bear, bison, rein- |
| |=Quaternary= |or “most recent.” |deer, musk-ox. |
| |(_kwa-ter´na-ri_) |Glacial Period. |Possibly man was |
| |or “fourth.” Once | |living but that is |
| |supposed to be the| |uncertain. |
| |_fourth_ sedimen- | | |
| |tary system. Age |=Pliocene= |Plants and animals |
| |of man. |(_plī´ō-sēn_), or |much as today, |
| | |“more recent.” |aside from human |
| | | |and domestic |
| | | |species. |
| +------------------+------------------+-------------------+
|=Cenozoic= | |=Miocene= (_mī´ō- |Land animals in- |
|(_se´nō-zō´- | |sēn_), or “less |clude elephants, |
|ik_), or | |recent.” |camels, deer, oxen,|
|“Recent | | |horses, true apes, |
|life.” | | |etc. Marine animals|
| | | |much like those to-|
|_Estimated | | |day. Among plants, |
|Age of | | |grasses become im- |
|Period_, | | |portant; deciduous |
|=3,000,000= | | |trees increase. |
|_years_. |=Tertiary= (_ter´-| | |
| |shi-a-ri_), or |=Oligocene= |Ancient dogs, cats,|
| |“third”. Once |(_ōl´ĕ-gō-sēn_), |rabbits, squirrels,|
| |supposed to be the|or “a little more |camels, and horses |
| |_third_ sedimen- |recent.” |were represented. |
| |tary system, or | | |
| |Age of mammals. | | |
| | |=Eocene= (_ē´-ō- |Mammals flourished,|
| | |sēn_), or “dawn of|including rodentia,|
| | |recent.” |carnivera, eden- |
| | | |tates, lemuroids, |
| | | |birds, reptiles, |
| | | |etc. Flora included|
| | | |figs, palms, |
| | | |bananas; willows, |
| | | |chestnuts, oaks, |
| | | |etc. |
+-------------+------------------+------------------+-------------------+
| | |{Upper. |Reptiles predomi- |
| | |{ |nate: turtles, |
| | |{ |lizards, |
| | |{ |crocodiles, flying |
| | |{ |reptiles, etc. Many|
| | |{ |waterbirds. Angio- |
| |=Cretaceous= |{ |sperms predominate:|
| |(_krē-ta´-she-us_)|{ |larch, beech, |
| |or “bearing |{ |walnut, tulip |
| |chalk.” |{ |trees, etc. |
| | |{ | |
|=Mesozoic= | |{Lower. |Reptiles abound. |
|(_mĕs-ō-zō´- | |{ |Flora includes |
|ic_), or | |{ |cycadeous, coni- |
|“Middle | |{ |fers, horsetails; |
|Life.” | |{ |angiosperms appear.|
| +------------------+------------------+-------------------+
|_Estimated | |{Upper. |Ammonites, belem- |
|Age of |=Jurassic= (_jȯȯ- |{ |ites continue in |
|Period_, |ras´sik_), or like|{ |great variety. |
|=5,000,000= |the mass of the |{Middle. |Reptiles numerous |
|_years_. |Jura Mountains. |{ |and varied types. |
| |Age of Reptiles. |{ |Flying reptiles and|
| | |{Lower. |reptile-like birds |
| | |{ |appear. |
| | | | |
| | |{Upper. |Reptiles of enor- |
| |=Triassic= |{ |mous size dominate |
| |(_trĭ-ăs´ĭk_), or |{ |the land and sea. |
| |in a triple |{Middle. |Mammals appear. |
| |series. |{ |Ammonites and |
| | |{ |belemites dominate |
| | |{Lower. |invertebrate life. |
+-------------+------------------+------------------+-------------------+
| | |=Permian= (_per´- |Reptiles become |
| | |mē-ăn_), like |prominent in number|
| | |those at Perm, |and variety; in- |
| | |Russia. |habit fresh water, |
| | | |salt water and |
| | | |land. |
| | | | |
| |=Carboniferous= |=Pennsylvanian=, |Plants abound. |
| |(_kăr-bŏn-if´-er- |like those of |Marked development |
| |us_), or coal- |Pennsylvania. |of land animals, |
| |bearing. Age of | |including insects, |
| |Amphibians. | |spiders and scorpi-|
| | | |ons. Lizards become|
| | | |important. Amphibi-|
| | | |ans reach climax. |
| | | | |
| | |=Mississippian=, |Crinoids greatly |
| | |or Lower Carboni- |developed. Am- |
| | |ferous. |phibians appear. |
| | | |Plant life expands.|
| +------------------+------------------+-------------------+
| | |{Upper. |Rapid changes in |
| | |{ |animal kingdom; |
| |=Devonian= (_de- |{ |shifting habitat; |
| |vō´ni-an_) like |{ |extensive develop- |
| |those of Devon- |{Middle. |ment of fishes; |
|=Paleozoic= |shire, England. |{ |sharks flourish. |
|(_pāl-æ-ô- |Age of Fishes. |{ |Plants are mainly |
|zō´ic_), or | |{ |small leaf and reed|
| “Old Life.” | |{Lower. |types. |
| +------------------+------------------+-------------------+
|_Estimated | |{=Ontarian= (_on- |Vertebrates appear;|
|Age of |=Silurian= (_si- |{tā´rē-ăn_), place|low forms of |
|Period_, |lū´ri-an_), in the|{name. |fishes. First reef |
|=24,000,000= |land of the |{ |building corals. |
|_years_. |Silures, England. |{=Champlainian= |Crinoids and bra- |
| |Age of In- |{(_shăm-plān´ē- |chiopods, important|
| |vertebrates. |{ăn_), place name.|Cephalopods con- |
| | |{ |tinue to dominate. |
| +------------------+------------------+-------------------+
| | |{=Cincinnatian= |Much as in the Cam-|
| | |{(_sĭn-sĭn-năt´-ē-|brian. Remains are |
| | |{ăn_), place name.|more abundant. |
| |=Ordovician= (_ŏr-|{ |Species more numer-|
| |dŏ-vīsh´ăn_), a |{=Mohawkian= (_mō-|ous; insects were |
| |place name in |{hŏk´ē-ăn_), place|present. Verte- |
| |Wales. |{name. |brates appear. Low |
| | |{ |forms of fishes. |
| | |{ |Trilobites reach |
| | |{ |climax. |
| +------------------+------------------+-------------------+
| | |{=Saratogan= |All great divisions|
| | |{(_săr-ă-tō´găn_),|of animal kingdom |
| | |{place name. |except vertebrates |
| |=Cambrian= (_kam´-|{ |are represented; |
| |bri-an_), from |{=Acadian= (_ä- |trilobites, bra- |
| |Cambria, the old |{kād´ē-ăn_), place|chiopods, sponges, |
| |name for Wales. |{name. |graptolites, etc. |
| | |{ |Little evidence of |
| | |{=Georgian= (_jōr´|vegetation, but it |
| | |{gē-ăn_), place |must have abounded |
| | |{name. |as food for |
| | |{ |animals. |
+-------------+------------------+------------------+-------------------+
|=Proterozoic=| |{=Keweenawan=, |Fossils rare or |
|(_prō-ter-ō- | |{(_kē´wē-năh- |wanting. |
|zō´ik_) or |=Algonkian= (_ăl- |{wān_), pertaining| |
|“Former |gŏn´kē-ăn_), from |{to Keweenaw Pen- | |
|Life.” |district of |{insula, Michigan.| |
| |Algonquin |{ | |
|_Estimated |Indians, north of |{=Huronian= (_hu- |Rocks contain clear|
|Age of |St. Lawrence. |{rō´nē-ăn,_), |evidence of low |
|Period_, | |{rocks on borders |forms of life. |
|=18,000,000= | |{of Lake Huron. | |
|_years_. | |{ | |
+-------------+------------------+------------------+-------------------+
| | |{=Laurentian= |Since the rocks are|
|=Archaeozoic=| |{(_law-ren´shi- |of igneous origin, |
|(_ar´kē-o-zō´| |{an_), pertaining |they contain no |
|ic_), “With- | |{to rocks along |organic remains. |
|out Life.” | |{the St. Lawrence | |
| |=Archean= (_är- |{River. | |
|_Estimated |kē´-ăn_), |{ | |
|Age of |“oldest.” |{=Keewatin= (_kē- |No fossils found, |
|Period_, | |{wā´tĭn_), rocks |but carbonaceous |
|=18,000,000= | |{in a district of |schists and lime- |
|_years_. | |{Manitoba, Canada.|stones are believed|
| | |{ |to indicate the |
| | |{ |presence of life. |
+-------------+------------------+------------------+-------------------+
+-------------+------------------+------------------+-------------------+
|=Life Ages | =Rock Systems= | =Series of | =Chief Economic |
|of the Earth=| | Rock Strata= | Products= |
+-------------+------------------+------------------+-------------------+
| | |Recent, or Human. |Clay, peat, bog |
| | | |iron ore, marl, |
| | | |gold placers. |
| |=Quaternary= | | |
| |(_kwa-ter´na-ri_) |=Pleistocene= |Clay, gravel, |
| |or “fourth.” Once |(_plīs´tŏ-sēn_), |gold placers. |
| |supposed to be the|or “most recent.” | |
|=Cenozoic= |_fourth_ sedimen- |Glacial Period. | |
|(_se´nō-zō´- |tary system. Age | | |
|ik_), or |of man. |=Pliocene= |Gold (in part |
|“Recent | |(_plī´ō-sēn_), or |placers), coal, |
|life.” | |“more recent.” |oil, gas. |
| +------------------+------------------+-------------------+
|_Estimated | |=Miocene= (_mī´ō- |Silver, gold, coal,|
|Age of | |sēn_), or “less |oil, gas, phosphate|
|Period_, | |recent.” |rock, diatomaceous |
|=3,000,000= |=Tertiary= (_ter´-| |earth. |
|_years_. |shi-a-ri_), or | | |
| |“third”. Once |=Oligocene= |Copper, silver. |
| |supposed to be the|(_ōl´ĕ-gō-sēn_), | |
| |_third_ sedimen- |or “a little more | |
| |tary system, or |recent.” | |
| |Age of mammals. | | |
| | |=Eocene= (_ē´-ō- |Gold, zinc, lead, |
| | |sēn_), or “dawn of|coal, oil, gas. |
| | |recent.” | |
+-------------+------------------+------------------+-------------------+
| |=Cretaceous= |{ |Coal, oil, gas, |
| |(_krē-ta´-she-us_)|{Upper. |copper, gold, china|
| |or “bearing |{ |clay, fire clay, |
| |chalk.” |{Lower. |cement building |
|=Mesozoic= | |{ |stone. |
|(_mĕs-ō-zō´- | |{ | |
|ic_), or | |{ | |
|“Middle +------------------+------------------+-------------------+
|Life.” |=Jurassic= (_jȯȯ- |{Upper. |Oil, gold. |
| |ras´sik_), or like|{ | |
|_Estimated |the mass of the |{Middle. | |
|Age of |Jura Mountains. |{ | |
|Period_, |Age of Reptiles. |{Lower. | |
|=5,000,000= | | | |
|_years_. | |{Upper. |Salt, gypsum, a |
| |=Triassic= |{ |little coal in |
| |(_trĭ-ăs´ĭk_), or |{Middle. |Virginia, copper, |
| |in a triple |{ |building stone. |
| |series. |{Lower. | |
+-------------+------------------+------------------+-------------------+
| | |=Permian= (_per´- |Salt and gypsum; |
| | |mē-ăn_), like |some coal in |
| | |those at Perm, |Eastern States. |
| | |Russia. | |
| | | | |
| |=Carboniferous= |=Pennsylvanian=, |Coal, oil, gas, |
| |(_kăr-bŏn-if´-er- |like those of |iron ore, fire |
| |us_), or coal- |Pennsylvania. |clay, phosphate |
| |bearing. Age of | |rock. |
| |Amphibians. | | |
| | | | |
| | |=Mississippian=, |Oil, gas, lead, |
| | |or Lower Carboni- |zinc, building |
| | |ferous. |stone, cement rock.|
| +------------------+------------------+-------------------+
| |=Devonian= (_de- |{Upper. | |
| |vō´ni-an_) like |{ |Gas, oil, iron ore,|
| |those of Devon- |{Middle. |phosphate rock. |
|=Paleozoic= |shire, England. |{ | |
|(_pāl-œ-ô- |Age of Fishes. |{Lower. | |
|zō´ic_), or +------------------+------------------+-------------------+
| “Old Life.” | |{=Ontarian= (_on- |Iron ore, gas, |
| |=Silurian= (_si- |{tā´rē-ăn_), place|salt, gypsum, |
|_Estimated |lū´ri-an_), in the|{name. |cement rock. |
|Age of |land of the |{ | |
|Period_, |Silures, England. |{=Champlainian= | |
|=24,000,000= |Age of In- |{(_shăm-plān´ē- | |
|_years_. |vertebrates. |{ăn_), place name.| |
| +------------------+------------------+-------------------+
| | |{=Cincinnatian= |Oil, gas, lead, |
| |=Ordovician= (_ŏr-|{(_sĭn-sĭn-năt´-ē-|zinc, phosphate |
| |dŏ-vīsh´ăn_), a |{ăn_), place name.|rock, manganese, |
| |place name in |{ |marble. |
| |Wales. |{=Mohawkian= (_mō-| |
| | |{hŏk´ē-ăn_), place| |
| | |{name. | |
| +------------------+------------------+-------------------+
| | |{=Saratogan= |Lead, zinc, barite,|
| | |{(_săr-ă-tō´găn_),|copper. |
| | |{place name. | |
| |=Cambrian= (_kam´-|{ | |
| |bri-an_) from |{=Acadian= (_ä- | |
| |Cambria, the old |{kād´ē-ăn_), place| |
| |name for Wales. |{name. | |
| | |{ | |
| | |{=Georgian= (_jōr´| |
| | |{gē-ăn_), place | |
| | |{name. | |
+-------------+------------------+------------------+-------------------+
| | |{=Keweenawan=, |Copper, silver. |
|=Proterozoic=| |{(_kē´wē-năh- | |
|(_prō-ter-ō- | |{wān_), pertaining| |
|zō´ik_) or | |{to Keweenaw Pen- | |
|“Former |=Algonkian= (_ăl- |{insula, Michigan.| |
|Life.” |gŏn´kē-ăn_), from |{ | |
| |district of |{=Huronian= (_hu- |Principal iron ores|
|_Estimated |Algonquin |{rō´nē-ăn,_), |of Lake Superior |
|Age of |Indians, north of |{rocks on borders |region; also |
|Period_, |St. Lawrence. |{of Lake Huron. |copper, nickel, |
|=18,000,000= | |{ |silver, cobalt, |
|_years_. | |{ |gold. Building |
| | |{ |stone and ornamen- |
| | |{ |tal stone. |
+-------------+------------------+------------------+-------------------+
| | |{=Laurentian= |Iron ores, precious|
|=Archaeozoic=| |{(_law-ren´shi- |metals, gems, |
|(_ar´kē-o-zō´| |{an_), pertaining |apatite, rare |
|ic_), “With- | |{to rocks along |earths, graphite, |
|out Life.” | |{the St. Lawrence |asbestos. |
| |=Archean= (_är- |{River. | |
|_Estimated |kē´-ăn_), |{ | |
|Age of |“oldest.” |{=Keewatin= (_kē- |Emery, building and|
|Period_, | |{wā´tĭn_), rocks |ornamental stones. |
|=18,000,000= | |{in a district of | |
|_years_. | |{Manitoba, Canada.| |
+-------------+------------------+------------------+-------------------+
[Illustration: =GEOLOGICAL MAP OF THE UNITED STATES SHOWING THE REGIONS
OF REPRESENTATIVE FORMATIONS=]