18770 Th e Loess of the Rhine and the Danube . 79 
the Irish elk in Europe and the mastodon in America, 
which have perished since the commencement of neolithic 
times, 
I have now given all the most important faCts that I know 
of respecting the position and distribution of the loess, and 
we may proceed to consider the theories that have been 
proposed to account for its origin. First of all we shall have 
to determine, as well as we may from the faCts before us, 
whether the loess was deposited in previously formed valleys 
which were as deep or deeper than they are now, or that it 
was laid down in the process of the excavation of the 
valleys. The former view was that held by Sir Charles 
Lyell, who had studied the loess both of the Rhine and 
the Danube, and who in his “ Antiquity of Man ” has given 
- — with the logical force and clearness that characterise all 
his writings — a most able summary of the faCts that influ- 
enced his judgment. These are, briefly, that the loess 
encircles some of the modern cones of loose pumice and 
ashes of the Lower Eifel ; that it rests on gravel near the 
bottoms of the present valleys ; and that there is evidence 
that before it was deposited there existed steep slopes, as 
between Darmstadt and Heidelberg, where loess 200 feet 
thick and reaching up to 800 feet above the river is banked 
up against an old valley slope composed of granitic rocks. 
Prof. Ramsay, on the contrary, favours the opinion that 
the loess of the Rhine has been deposited by the river, 
which, as it gradually lowered the level of the plain, left its 
finer detritus at various heights above it.* The memoir in 
which this opinion is expressed is an essay to prove that 
the valley of the Rhine has been excavated by the river, — ■ 
an opinion not likely to be disputed by any geologist. The 
question of the deposition of the loess is only incidentally 
mentioned, and no explanation is offered of the many faCts 
advanced by Dr. Hibbert, Sir Charles Lyell, and others, to 
prove that before such deposition commenced the valley had 
been excavated to at least its present depth. The authority 
of the Director of the Geological Survey of England is so 
great that it is necessary to insist here upon the cogency of 
the arguments that have been urged against the theory he 
espouses, and it is a pity that he has not met them or even 
alluded to them in his memoir. We have already seen that 
the loess rests on previously deposited beds of gravel. At 
Wurzberg this gravel lies at only a slight elevation above 
* Quart. Journ. Geol. Soc., vol. xxx., p. 89. 
