* * * * *
=INTRODUCTION.=
The present paper is designed to give the results of some field-work
in southern Algeria in the autumn of 1910 and the spring of 1911. The
chief purpose of the tour was to examine the more obvious features
of the physiological conditions prevalent in the region in question
and, in connection with these observations, to make some detailed
studies of the root-habits of the most striking species of the
native flora. The route lay through the Atlas Mountains, over
the High Plateau, and for some distance into the Sahara itself,
returning by a somewhat similar way farther to the east. The country
traversed was extremely varied in topography and in plant life, and
probably the most southern regions seen may be taken as typical of
much of the western Sahara. The distance covered in the more arid
portions of the colony was about 1,000 miles.
An English-speaking tourist, or any tourist for that matter,
is something of a curiosity in southern Algeria. We were said to
be the second party of “Englishmen” who had passed over the
Ghardaia-Ouargla country in twenty-five years.
Leaving Algiers in October, diligence was taken to Ghardaia, the
most important town in southern Algeria and the end of the diligence
service. Beyond Ghardaia travel is by camel only. The diligence
journey, if made without stop, requires six days, running night and
day, except the first day’s run, which is by day only. Pauses in
the journey to Ghardaia were made at the leading towns or stage
stations (bordj), thus affording opportunity to observe several
localities in the High Plateau as well as the portion of the desert
just south of the Saharan Atlas. Stop-overs were made thus at Medea,
Boghari, Djelfa, Laghouat, and Tilrempt. A fortnight was passed
at Ghardaia, where the environs of the city were quite thoroughly
explored. As there are no roads between Ghardaia and Ouargla,
or between Ouargla and Touggourt, it was necessary to organize a
small camel-train, engage a cameleer (sokhrar) and servants, and
make special arrangements for the trip. Nine days were required for
the portion of the journey to Touggourt via Ouargla. At Touggourt
diligence was again taken for Biskra, two days’ journey. The
return journey to Algiers from Biskra was broken at Batna for the
purpose of visiting the fine forest of cedar (_Cedrus atlantica_)
in the mountains not far from the town. When Biskra was revisited,
in the spring of 1911, the northern portion of Algeria was crossed
on the way from Tunis, this affording an opportunity to observe
something of the picturesqueness of the mountainous regions as well
as the spring flora.
I wish to take this early opportunity to acknowledge my appreciation
of assistance received from different persons during the course
of the Algerian study, or as a means of preparing for it. I
am especially indebted to Prof. H. J. Hall, of Leland Stanford
University, who was my companion in Algeria and whose knowledge of
the American deserts made his advice doubly valuable. Dr. Keltie,
secretary of the Royal Geographical Society, provided letters
and information of much use. Dr. Trabut, government botanist
of Algeria, whose acquaintance with the country is extensive,
very kindly identified all plants sent him and gave valuable aid
in other ways. The map (plate A) was prepared expressly for this
study by Mr. Godfrey Sykes.
In a country where travel away from the beaten path is not without
discomfort, it is important that the way be made as smooth as
possible, not alone for comfort but for personal safety as well,
and it is therefore a pleasure to acknowledge the many kindnesses
shown by the civil and military authorities of the French colony,
as also by the American consul and vice-consul at Algiers.
=GEOGRAPHICAL CHARACTERISTICS OF ALGERIA.=
The French colony of Algeria is of large extent and possesses a
highly varied topography and great range in climate. With an all-land
connection with the continent of Europe in earlier geologic times,
the flora and fauna of this portion of northern Africa are closely
allied to the fauna and flora of southern Spain, France, and Italy.
Algeria lies to the south of the Mediterranean Sea, between Tunis
to the east and Morocco to the west. The northern portion extends
somewhat beyond latitude 37°, or that of southern Spain, southern
Greece, and the southern part of Asia Minor. The limit of the colony
on the south is indefinite, reaching to about latitude 21°. Thus
east and west the extent is about 650 miles, and north and south
1,200 miles.
The most important topographical features of the northern part of
Algeria are the several mountain masses which together constitute the
Atlas range. Lowest in Tunis, where the Atlas Mountains do not exceed
5,000 feet altitude, they attain their greatest height in Morocco,
over 13,000 feet. In Algeria an altitude of about 7,500 feet is
reached in the Aurés, Dj. Chelia, and in the Great Kabylies. In
the eastern portion of Algeria the mountains extend to the coast,
but farther west a narrow strip of lowland separates them from the
sea. In the east (in the department of Constantine) they constitute
a single general uplift, although made up of several groups, but
as one proceeds westward the mountains separate into two ranges,
which at the Morocco border are about 125 miles apart. The two
ranges have been called by various names, among which are the
Great Atlas for the southern range and the Little or Maritime Atlas
for the northern one. But it seems best to use the names Atlas of
the Sahara or Saharan Atlas and Atlas of the Tell or the Tellian
Atlas, names which are self-explanatory. The Tellian Atlas and all
territory between this range and the Mediterranean Sea is known as
the Tell, or the land of hills. This is the most important part of
Algeria from an agricultural standpoint, and furnishes grain and
other products. Here also are the most important forests, oak,
pine, and cedar. Between the two ranges of the Atlas lies the
region of the steppes or plateaus, in this study referred to as
the High Plateau, inasmuch as the average altitude is over 3,000
feet. The steppe region is highest in the west and is wedge-shaped,
in conformity to the bounding mountains. In the eastern portion it
breaks up into mountain valleys. The topography of the High Plateau
is monotonous. The surface is gently rolling, and here and there
are undrained depressions, or _chotts_, where salts accumulate. In
rainy seasons the chotts contain water, but in the arid summers they
are dry. The region of the steppes is of no agricultural value,
although, as will appear below, the harvesting of the alfa grass,
which occupies vast areas, is of considerable importance.
South of the Saharan Atlas lies the desert, comprising about
2,000,000 square miles, the topography of which is extremely
varied. For present purposes it is sufficient to say that in the
extreme southern portion of the Algerian Sahara, and crossed by the
Tropic, there is an extensive highland, the plateau of Idghagh,
where an elevation exceeding 5,000 feet is reached. All of the
Sahara to the west of this plateau, or to the west of a line drawn
north from it, appears to be above sea-level (much of it having an
altitude of 1,000 feet), and of greater geological age than that
portion of the desert lying to the east. North from the plateau of
Idghagh the country gradually descends to the depression of which
the great Chott Melghir is a part, a region below the level of
the sea. Here extends also one of the longest oueds of the Sahara,
the Oued Igharghar, which takes its rise in the plateau of Idghagh
and empties in the Chott Melghir, an entire length exceeding 700
miles. In the western part of the Sahara the surface descends to the
Atlantic, but in the eastern part it falls away to the Mediterranean.
Turning now to consider the part of southern Algeria with which
this study especially deals—lying between Laghouat and Ghardaia,
between Ghardaia and Ouargla, and between the latter place and
Biskra, all to the south of the Saharan Atlas—we find topographical
details which are probably representative of much of the rest of
the Great Desert. Laghouat has an elevation of 2,400 feet. It lies
on the northern edge of the region of the dayas. This region is
characterized by the poor development of its drainage and has a
slightly undulating surface with frequent depressions, each the
center of an area of rather small extent, from which it receives
flood-waters. The dayas differ from the other undrained areas,
the chotts, in that they do not contain an excess of salt, owing
probably to efficient subdrainage. In the region of the dayas the
surface falls away to the south or the southeast until the region
of the Chebka is reached, which extends to the territory of the
Beni M’Zab. In the Chebka low and flat-topped mountains are so
irregularly disposed as to give rise to the name, meaning a net;
they are separated by valleys, narrow toward the northern portion
of the region, but expanding into small plains as one proceeds
towards Ghardaia. Ghardaia, the country of the Beni M’Zab,
marks the southern limit of the Chebka. At Ghardaia the altitude
is 1,600 feet. Between Ghardaia and Ouargla are undulating stony
plains, the Gantara (_hamada_), large salt spots, the chotts, and
a prominent range of sand mountains, _areg_ desert, possibly 1,000
feet high. At the eastern edge of the Gantara the general level
of the country drops suddenly about 200 feet to the Ouargla plain
(_reg_ desert), with an altitude less than 500 feet; this is an
eroded flood-plain of the Oued Igharghar or its tributaries.
There are no navigable rivers in Algeria. The most important river
is the Chelif, which takes its origin in the Saharan Atlas, crosses
the High Plateau, breaks through the Atlas of the Tell, and, turning
westward, traverses obliquely the Tell for a distance of about 108
miles before discharging into the sea. The Chelif is the only stream
which rises in the Saharan Atlas and pierces the northern range. To
the south of the Saharan Atlas are several important oueds. One,
the Oued Djedi, rises near Aflou and goes easterly, past Laghouat,
until it reaches the Chott Melrir, south of Biskra; two others, the
M’Zab and the Nessa, drain the region of the Chebka, and taking
an easterly or a southeasterly direction reach the Oued Rirh or its
upper extension. The Oued Rirh constitutes the northern portion of
the great Oued Igharghar, or a tributary of this oued, and extends
about 60 miles north from Touggourt to the Chott Merouan. The region
of the Oued Rirh is of great economic importance from the production
of dates, made possible through the development of artesian wells
by the French government. The oueds as a whole are very like the
arroyos of the southwestern portion of the United States, in that
they carry water for a small portion of the year only, when the
torrential rains fill them with a muddy, rushing flood.
In the plains adjacent to the oueds, at Ghardaia especially, the
natives usually dig their wells, from which water for domestic as
well as for irrigating purposes is obtained. The flood-water of
the oueds is also diverted into ditches, or impounded for later
use, although the latter has not met with uniform success. The
depths at which water has been found vary greatly. At Ouargla the
water lies within 3 feet of the surface, although there are also
very deep artesian wells, and at Ghardaia it varies from 10 to
50 feet or more. At the daya of Tilrempt the water in the deepest
wells stands as deep as 300 feet; it is drawn in a very primitive
fashion for purposes of watering flocks and for the bordj. The
heaviest vegetation is to be found along the oueds and the nearby
flood-plains. Here the water relations are the most favorable and
the oueds constitute highways along which plants venture into the
desert from the more humid regions.
Very little study appears to have been given the soils of Algeria. It
has been stated that there are vast areas of light, sandy soils, and
also extensive tracts of marls, clays, and alluvial soils.[1] Gypsum
is an important element in the soils, both those of the oases and
probably of the open desert also; it occurs in great quantity in
the large chotts of the desert, along with common salt and other
salts. In the soils of the oases it acts as a cementing material,
“uniting the finer soil-grains into aggregates which give the
soil a much more sandy appearance than would be suspected from the
results of mechanical analysis.” At Laghouat and at Ghardaia a
light-colored, hard substance, closely resembling the “caliche”
of the southwestern United States, was seen incrusting stones,
filling cracks in rocks and crevices between rocks, and in places
forming a stratum, horizontally placed (15 cm. more or less in
thickness) underneath the superficial soils. This is extremely
hard and can be broken or cut with difficulty. In the valley of the
M’Zab, where it constitutes a heavy substratum, it appears to be
impervious to water. This hardpan is used as threshing floors by
removing the superficial soils.
An unexpectedly small amount of sand was observed over the route
traversed. Near the southern edge of the High Plateau a sand belt
was encountered and a long stretch of low dunes was seen leading
to the eastward, which were said to reach nearly to Bou Saada; and
again at Laghouat there are dunes to the east of town as well as
to the west. Low dunes were seen in the valley of the Oued M’Zab,
and sand mountains, possibly 250 meters high, were passed on the way
from Ghardaia to Ouargla. Between Ouargla and Touggourt, also, sand
was encountered and the way lay across about 12 miles of low dunes;
to the north of Touggourt dunes are also to be seen; and finally,
some sand is to be found in the neighborhood of Biskra. Although,
thus, relatively little sand was met, much of the entire portion
of southern Algeria is covered by sand. Large areas of sand-covered
country lie to the east of the Oued Rirh, and especially southeast
of Touggourt, and also to the west of Ghardaia there is said to
be a large dune-covered territory. For the most part, however,
the surface of the plains crossed is covered with large or small
stones, mingled with which, or beneath which, there is a rather fine
clay-like soil. This constitutes the hamada, or stony desert, of
which the largest portion of the surface of the Sahara is probably
composed. Where stones are largely absent and the soil is fine,
usually of fluvian origin, the formation is known as “reg.” Reg
desert was encountered at and north of Ouargla, in the drainage of
the Igharghar or its tributaries, and south of Biskra. The latter
may not, strictly speaking, be reg, but a wide-stretching bajada,
and the soil is probably only in small part deposited by rivers.
=CLIMATE OF ALGERIA.=
The climate of Algeria is mild and temperate. This is due to several
factors, among which are its situation relative to the Mediterranean
on the north and to the Atlantic on the west, as well as to the great
desert which constitutes its southern portion, the great variation
in topography, and the fairly low latitude. Taking the colony as
a whole, there is a great range in temperature, precipitation,
relative humidity, and evaporation, to mention only such climatic
features as have been reduced and are recorded; and the range in the
intensity and in the quality of the light must also be great. The
climate of the northern portion of Algeria is coastal, while that
of the southern portion is continental.
The distribution in time and in space and the amount of precipitation
are of the greatest importance as climatic features of Algeria. The
rainfall is heaviest on the littoral, and especially heavy in the
eastern portion of the littoral. An average of 1,000 mm. is reported
from the immediate vicinity of the sea,[2] and as one goes southward
the amount of precipitation rapidly becomes less. In the Tell the
average rainfall is 570 mm., while on the High Plateau it is 310
mm. On the desert the rainfall is uncertain both in amount and
in time, except that when rains occur the time coincides with the
rainy season of northern Algeria. At Biskra the annual precipitation
is 199 mm., at Laghouat it is 198 mm., at Ghardaia it is 114 mm.,
and at El Golea it is 47 mm. In many places in the western Sahara,
five years or more go by without fall of rain.
The differences in the geographical distribution of precipitation
vary from year to year, as may be illustrated by referring to that
for the year 1908, which may be compared with the normal usual
distribution as given above. In the northern portion of the country
more rain than usual was reported; for example, there was over 1,000
mm. on the littoral east of Algiers, and over 500 mm. on the High
Plateau, but on the desert the amount was somewhat less. At Laghouat
it was 161 mm., at Ghardaia it was 89.2 mm., and at Ouargla it was
28 mm.
Besides the differences in amount of yearly rainfall, well-marked
seasonal amounts of precipitation are also to be noted. In the
northern portion of the colony rains are likely to occur in winter
and spring, the summer and early autumn being dry; and as one goes
south of the Saharan Atlas nearly the same conditions obtain; that
is, the rains usually fall during the rainy season of the coast. The
seasonal distribution of rain for the Tell, including the stations
of the littoral, the High Plateau, the Saharan Atlas, and the desert,
for a series of years including 1908, is given in table 1.