A HISTORY OF CUMBERLAND 
after the prolonged period of subsidence, during which the Silurian 
Rocks were formed, the sea bottom remained for a time stationary, then 
began a set of earth movements which, at great depths, gradually and 
quietly compressed the lately-formed strata into folds, closer and closer, 
as the compression continued, and at the same time the lateral thrusts 
forced up the surface, so that by degrees great ridges of considerable 
extent were elevated above the level of the sea. Narrow areas of sea 
water were thus isolated by the upheaval, and gradually passed from the 
condition of lagoons into that of shallow inland lakes. As the movement 
extended, the whole of the part under notice gradually passed into the 
state of a continental area, from which the sea margin receded farther 
and farther as the upheaval slowly progressed. One of the consequences 
of these conditions was that the annual rainfall gradually decreased in 
amount, and fell only at irregular and often distant intervals. As a 
consequence, vegetation could no longer thrive; land animals, such as 
there were at the time, were forced to migrate to districts where the cli- 
matal conditions were more favourable; and hence, by degrees, the whole 
area gradually passed into an upland desert region far removed from the 
sea. When it did happen to rain the amount precipitated in a given 
time was often very large ; so that after one of these occasional thunder- 
storms roaring torrents were quickly formed, and soon tore their way 
down the hill slopes, thereby spreading great masses of torrential debris 
on the plains around. In the intervals between these spates the dry 
climate gave rise to great diurnal extremes of temperature, which caused 
any rocks exposed to their influence to expand rapidly with the heat 
during the day and to contract to the same extent at night, as a con- 
sequence of the rapid radiation which always takes place where there is 
but a small amount of moisture in the air. In other words, the lately 
formed marine sediments, now consolidated into stone, were shivered 
into fragments by the diurnal extremes of temperature, in much the same 
manner as they are in the Syrian wadies of to-day. The wind blew the 
rock fragments about from place to place, bowling them along and 
against each other until they were worn into perfectly-rounded grains, 
and it finally heaped these sands up in great ridges much as it does in 
all desert regions to-day. 
Lakes were represented here and there by a few shallow pools, each 
one of the same nature as the schatts of Algeria, or the shallow inland 
lakes of the Aralo-Caspian area of Central Asia, and containing more or 
less saline waters, such as are now to be found in desert regions in various 
parts of the world. There is no reason to suppose that the average daily 
temperature was higher than we experience in these islands now, but the 
maxima and minima were much greater, and it was certainly much hotter 
in the sun of a day and equally colder at night, and in this respect more 
like the climate of Natal than it is with us now. 
Analogy with modern desert areas quite warrants us in picturing to 
our mind’s eye the skies of these days in ancient Cumberland as usually 
cloudless, and as characterized rather by a yellow haze, due to the vast 
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