152 
NEWER PLIOCENE PERIOD. 
[Ch. XI. 
often containing calcareous sandy concretions or nodules, rarely 
exceeding the size of a man's head. Its entire thickness, in 
certain localities, amounts to several hundred feet ; yet no signs 
of stratification appear in the mass, except here and there at 
the bottom, where there is a slight intermixture of materials 
derived from subjacent rocks. No marine remains are any- 
where imbedded in it, but land- shells of existing species are 
extremely common, and the remains of the mammoth, horse, 
and some other quadrupeds, are said to have been found in it. 
The general absence of fresh- water shells is very remarkable. 
I collected a few specimens in the section near the Manheim 
gate of Heidelberg, and they are mentioned as having been 
found at a few other spots, by several of the writers above 
cited. 
The loess sometimes rises to the height of 300 feet above the 
alluvial plain of the Rhine, and to the height of 600 feet above 
the sea ; but it is confined to the valley of the Rhine and its 
tributary valleys, preserving everywhere the same mineral cha- 
racters, except where the lowest portion is mixed up, as before- 
mentioned, with matter derived from the underlying rocks. 
The loess reposes on every rock, from the granite to the gravel 
of the plains of the Rhine, and must have been thrown down 
from some vast body of water, densely charged with sediment, 
after the country had assumed its pi'esent configuration. I 
am informed by M. Studer, that it does not extend into 
Switzerland, so that we may suppose the flood to have de- 
scended from near the borders of that country, perhaps from 
the neighbourhood of Basle, into the valley of the Rhine, where 
one of the first great obstacles to its passage would be the 
Kaiserstuhl, a small group of volcanic hills which stand almost 
in the middle of the plains of the Rhine, south of Strasburg, 
between the chains of the Black Forest and the Vosges. These 
hills are covered nearly to their summits with loess. But the 
narrow gorge of Bingen and Andernach would cause the 
greatest obstruction, even if we suppose that defile to have been 
open when the flood descended, which was probably the case, 
