RECENT AND POST-PLIOCENE DEPOSITS. 
151 
The situation of the shell-mounds and lake-dwellings above 
alluded to is such as to imply that the topography of the 
districts where they are observed has not subsequently un¬ 
dergone any material alteration. Whereas we no sooner ex¬ 
amine the Post-pliocene formations, in which the remains of 
so many extinct mammalia are found, than we at once per¬ 
ceive a more decided discrepancy between the former and 
present outline of the surface. Since those deposits origi¬ 
nated, changes of considerable magnitude have been effect¬ 
ed in the depth and width of many valleys, as also in the di¬ 
rection of the superficial and subterranean drainage, and, as 
is manifest near the sea-coast, in the relative position of land 
and water. In the annexed diagram (Fig. 87) an ideal sec- 
1. Peat of the recent period. 2. Gravel of modern river.^ 2'. Loam of bricTc-earth 
(loess) of same age as 2, formed by inundations of the river. 3. Lower-level 
valley-gravel with extinct mammalia (Post-pliocene). 3'. Loam of same age. 
4. Higher-level valley-gravel (Post-pliocene). 4'. Loam of same age. 5. Upland 
gravel of various kinds and periods, consisting in some places of unstratilied 
boulder clay or glacial drift. C. Older rocks. 
tion is given, illustrating the different position which the 
Kecent and Post-pliocene alluvial deposits occupy in many 
European valleys. 
The peat, No. 1, has been formed in a low part of the mod¬ 
ern alluvial plain, in parts of which gravel No. 2 of the re¬ 
cent period is seen. Over this gravel the loam or fine sedi¬ 
ment 2' has in many places been deposited by the river dur=- 
ing floods which covered nearly the whole alluvial plain. 
No. 3 represents an older alluvium, composed of sand and 
gravel, formed before the valley had been excavated to its 
present depth. It contains the remains of fluviatile shells 
of living species associated with the bones of mammalia, in 
part of recent, and in part of extinct species. Among the 
latter, the mammoth {JE, prhnigenms) and the Siberian rhi¬ 
noceros {R, tichorhinus) are the most common in Europe. 
No. 3' is a remnant of the loam or brick-earth by which No. 
3 was overspread. No. 4 is a still older and more elevated 
terrace, similar in its composition and organic remains to 
No. 3, and covered in like manner with its inundation-mud. 
