VERTICAL STRATIFICATION. 
73 
tween land, fresh-water, and marine fossils as to enable the 
geologist to determine whether particular groups of strata 
were formed at the bottom of the ocean or in estuaries, riv¬ 
ers, or lakes. If surprise was at first created by the discov¬ 
ery of marine corals and shells at the height of several miles 
above the sea-level, the imagination was afterwards not less 
startled by observing that in the successive strata com¬ 
posing the earth’s crust, especially if their total thickness 
amounted to thousands of feet, they comprised in some parts 
formations of shallow-sea as well as of deep-sea origin ; also 
beds of brackish or even of purely fresh-water formation, as 
well as vegetable matter or coal accumulated on ancient land. 
In these cases we as frequently find fresh-water beds below 
a marine set or shallow-water under those of deep-sea ori¬ 
gin as the reverse. Thus, if we bore an artesian well below 
London, we pass through a marine clay, and there reach, at 
the depth of several hundred feet, a shallow-water and fiu- 
viatile sand, beneath which comes the white chalk originally 
formed in a deep sea. Or if we bore vertically through the 
chalk of the Korth Downs, we come, after traversing marine 
chalky strata, upon a fresh-water formation many hundreds 
of feet thick, called the Wealden, such as is seen in Kent and 
Surrey, which is known in its turn to rest on purely marine 
beds. In like manner, in various parts of Great Britain we 
sink vertical shafts through marine deposits of great thick¬ 
ness, and come upon coal which was formed by the growth 
of plants on an ancient land-surface sometimes hundreds of 
square miles in extent. 
Vertical, Inclined, and Curved Strata. —It has been stated 
that marine strata of different ages are sometimes found at a 
considerable height above the sea, yet retaining their orig¬ 
inal horizontality ; but this state of things is quite exception¬ 
al. As a general rule, strata are 
inclined or bent in such a manner 
as to imply that their original po¬ 
sition has been altered. 
The most unequivocal evidence 
of such a change is afforded by 
their standing up vertically, show¬ 
ing their edges, wfoich is by no 
means a rare phenomenon, espe¬ 
cially in mountainous countries. 
Thus we find in Scotland, on the southern skirts of the 
Grampians, beds of pudding-stone alternating with thin 
layers of fine sand, all placed vertically to the horizon. 
When Saussure first observed certain conglomerates in a 
4 
Fig. 54. 
Vertical conglomerate and sand¬ 
stone. 
