122 LOESS OF THE VALLEY OF THE KHINE. [Ch. X. 



the time when that basin had ah-eady acquired its present outline of hill 

 and valley. I allude to the. deposit provincially termed loess in part of 

 Germany, or lehm in Alsace, filled with land and freshwater shells of 

 existing species. It is a finely comminuted sand or pulverulent loam of a 

 yellowish gray color, consisting chiefly of argillaceous matter combined 

 wdth a sixth part of carbonate of lime, and a sixth of quartzose and 

 micaceous sand. It often contains calcareous sandy concretions or nod- 

 ules, rarely exceeding the size of a man's head. Its entire thickness 

 amounts, in some places, to between 200 and 300 feet; yet there are 

 often no signs of stratification in the mass, except here and there at the 

 bottom, where there is occasionally a slight intermixture of drifted ma- 

 terials derived from subjacent rocks. Unsolidified as it is, and of so 

 perishable a nature, that every streamlet flowing over it cuts out for 

 itself a deep gully, it usually terminates in a vertical clift', from the sur- 

 face of which land-shells are seen here and there to project in relief. In 

 all these features it presents a precise counterpart to the loess of the 

 Mississippi. It is so homogeneous as generally to exhibit no signs of 

 stratification, owing, probably, to its materials having been derived from 

 a common source, and having been accumulated by a uniform action. 

 Yet it displays in some few places decided marks of successive deposi- 

 tion, where coarser and finer materials alternate, especially near the bot- 

 tom. Calcareous concretions, also inclosing land-shells, are sometimes 

 arranged in horizontal layers. It is a remarkable deposit, from its posi- 

 tion, wide extent, and thickness, its homogeneous mineral composition, 

 and freshwater origin. Its distribution clearly shows that after the great 

 valle)^ of the Rhine, from Schaff"hausen to Bonn, had acquired its present 

 form, having its bottom strewed over with coarse gravel, a period arrived 

 when it became filled up from side to side with fine mud, probably de- 

 posited during river inundations ; and it is also clear that similar mud 

 and silt were thrown down contemporaneously in the valleys of the prin- 

 cipal tributaries of the Rhine. 



Thus, for example, it may be traced far into Wiirtemberg, up the val- 

 ley of the Neckar, and from Frankfort, up the valley of the Main, to 

 above Dettelbach. I have also seen it spreading over the country of 

 Mayence, Eppelsheim, and Worms, on the left bank of the Rhine, and 

 on the opposite side on the table-land above the Bergstrasse, between 

 Wiesloch and Bruchsal, where it attains a thickness of 200 feet. Near 

 Strasburg, large masses of it appear at the foot of the Yosges on the left 

 bank, and at the base of the mountains of the Black Forest on the right 

 bank. The Kaiserstuhl, a volcanic mountain which stands in the middle 

 of the plane of the Rhine near Freiburg, has been covered almost everv- 

 where with this loam, as have the extinct volcanoes between Coblentz 

 and Bonn. Near Andernach, in the Kirchweg, the loess containing the 

 usual shells alternates with volcanic matter ; and over the whole are 

 strewed layers of pumice, lapilli, and volcanic sand, from 10 to 15 feet 

 thick, very much resembling the ejections under which Pompeii lies 

 buried. There is no passage at this upper junction from the loess into 



