NOTE.--The location of the coal-fields and collieries mentioned in
the following pages may be seen on an accompanying map.
Under the head of Economic Geology, I shall describe with more detail
the mineral beds which have a commercial value, and in the following
order:--I. Coal; II. Iron Ore; III. Granite, Limestone, and Marble; IV.
Precious and Base Metals.
[Sidenote: Thickness of the Coal Measures.]
I. COAL.--The thickness of the Coal Measures of the Puget Sound basin is
estimated by Bailey Willis at something like 14,000 feet, though he
admits the obvious possibility of error in the calculation by reason of
undiscovered faults. We may fairly expect them, however, to be thicker
than the same group in the Rocky Mountains, which measure about 9,000
feet. As heretofore remarked, the sediments become thinner from west to
east. Of course, the maximum thickness is not to be expected in every
locality. Mr. Willis's estimate was made in the Wilkeson and Green River
fields, and really did not reach the limit of the coal-bearing rocks.
The coal rocks of the Cedar River and Snoqualmie basin have never, so
far as I know, been estimated, but probably this group is equal in
thickness to that of any other part of the field. The difficulty of
measurement arises from the numerous fractures and changes of strike
which exist.
[Sidenote: Fifteen workable seams.]
The number of distinct workable seams of coal of three feet and upwards,
belonging to the measures, may safely be put down at not less than
fifteen.
[Sidenote: Different kinds of coal described.]
Before considering the quality of these coals, I will, for better
understanding, make some prefatory statements in regard to the character
of coals generally. Charcoal has greater purity than mineral coals
usually have, because there is nothing in the charcoal except what
naturally belongs to the woody matter. Mineral coal, however, having
been buried in water, mud, and sand, must, almost of necessity, have
some mixture of foreign matter, either slate, which is simply hardened
mud; silica, which may have been derived from sand; iron and sulphur,
some of which may have been in the wood, but most of it, probably,
introduced in solutions; to which should be added, unexpelled oxygen,
which is not only useless as fuel, but which combines with a portion of
the contained hydrogen, and forms water in the substance of the coal.
The proportion of ash in coals of the same class is usually determined
by the amount of slate in the coal, in addition to the mineral matter
which belonged originally to the vegetable material from which the coal
was formed. In the pure state, the proportion of ash increases as the
transformation of woody fibre goes on from peat to anthracite.
[Sidenote: The chemical changes in coal beds.]
It is worth while to note what are the changes which take place in the
vegetable matter during the process. It may be described in a word as a
progressive loss of oxygen, and by this loss the coal becomes richer,
for the reason just given. The deoxidizing process is carried on by
means of chemical changes in the substance of the coaly matter. The
oxygen combining with a certain proportion of the carbon, forms carbon
di-oxide, or carbonic acid gas; and a certain other portion, combining
with hydrogen, forms water. Both of these are volatile in their
character, and gradually escape. Another loss is effected by the
combination of hydrogen and carbon, forming marsh gas. We have deadly
proof that these combinations are in progress in all coal mines by the
occurrence of "choke-damp" and "fire-damp," which are the miners' names
for these gases.
[Sidenote: Deficient nomenclature.]
Unfortunately, we have no settled nomenclature for the varieties of
coal, excepting the broad names lignite or brown coal, bituminous coal,
and anthracite. Even the term "bituminous" is scientifically inaccurate,
there being, in fact, no bitumen in any coal. But it is applied to such
coals as contain more oxygen and volatile combustible matter and water
than anthracite, and less of these elements than lignite. The term
lignite is made to include a great variety of substances, covering the
lignites of the Juro-Trias of James River (Dutch Gap), which retain not
only the structure, but the appearance of decaying wood; the lignites of
the State of Mississippi, which are of the same geologic age as those of
the Rocky Mountains, but which, owing to their watery and crumbly
character, are unfit for market; the lignites of the Grand and Moreau
rivers of Dakota, which are reported to have no commercial value; the
lignites of Bozeman, Montana, which are really valuable, but soon break
down into chips and grits; the lignites of Green River, Wyoming, which
are firm, bright, lump coals; and the lignites of King County,
Washington Territory, many of which are hard, bright, steam and shipping
coals. And when brought to the laboratory, it is found that chemically
these lignites vary even more than they do optically.
[Sidenote: Lignite an unsuitable name for the coals of Washington
Territory.]
This want of a varied nomenclature is to be regretted, because it
sometimes handicaps a good coal with an inferior name. It is only of
late that the Laramie or Cretaceous coals of Washington Territory have
been divided into lignites, bituminous coals, and anthracites. These
grade into each other so insensibly that it would be impossible to
classify them sharply. None of the lignites which I saw were as low in
grade as the typical lignite. The woody structure was quite discernible
in some samples of the Franklin coal, and less in the Newcastle and
Green River; but in respect to the two latter, I could not with the
naked eye discern more of the woody structure than I have seen in some
of the West Virginia coals, which belong to the Carboniferous period. I
sat by fires of Newcastle and neighboring coals for a month, and
observed no unusual amount of smoke, and no peculiar odor. By analysis,
these coals show a larger percentage of oxygen than the typical
bituminous coal, but decidedly less than is found in the brown coal of
Germany, or in some of the lignites of Montana. They need a new name.
Their heating power is not so great as that of the bituminous coals of
the same region. Their streak and powder are less black, and their
fracture more conchoidal, but not decidedly so.
The bituminous coals have the usual cubical fracture. The Wilkeson
readily breaks down into small cubes. The lignites are black and
lustrous. They come out as lumpy as ordinary coal, and, when exposed to
weather, do not break up into powder and grits like ordinary lignite.
This is true, at least, of the Newcastle coal.
[Sidenote: The coking quality not general in these coals, but found in
some.]
The coking quality of these coals cannot be determined by calculating
the proportion between the fixed carbon and the volatile, combustible
matter. I am not sure that Professor Fraser's fuel ratio tables are a
safe guide in any case. So far as now known, only a few of the
Washington Territory coals can be made into good coke. On this point,
however, we have only laboratory and rough field tests, excepting at the
Wilkeson mines, where twenty-five ovens were turning out a superior
quality of coke, as proved by every test save the use of it in high
furnace stacks, in which there had been no opportunity for trial. It is
claimed by many persons that seams on Green River, Skagit, Yakima, and
Snoqualmie will furnish good coking coal. The coal on Snoqualmie
Mountain, near Hop Ranch, has not been studied, but it certainly has the
external characteristics of good coking coal, and Mr. Peter Kirke made a
rough trial of it in an earth-pit with decidedly encouraging results.
Somewhat similar coal is found on Raging River, but where opened, so
much slate was interleaved with the coal that washing would be necessary
before use. More will be said hereafter with regard to these coals; but
the remark may be repeated here in respect to the entire Puget Sound
basin, that much additional examination is necessary before its coals
will be fully understood. The variations in character of these are not
owing entirely, or even chiefly, to their relative ages, but also to the
conditions to which they have been subjected, especially in respect to
heat. This metamorphic agency has acted not only in the body of the
Cascade Mountains, but all through the coal-fields, where faults,
flexures, and intrusive rocks have occasioned changes in the original
condition of the coal-beds, giving results along the whole scale of
metamorphism from lignite to anthracite.
[Sidenote: Analyses of Washington Territory coals.]
I here introduce (on the opposite page) a table of analyses made in
Washington City from representative samples of Washington Territory
coals and lignites selected by Mr. Bailey Willis during the examination
which he made of this field for the Census Bureau, and found in Vol. XV.
of the Census Reports.