296 Prof. Baron F. RichtJiofen — On the Origin of the Loess. 



This shape of surface is precisely similar to that which is character- 

 istic of the salt steppes of Central Asia. It must, however, be re- 

 marked that, just as in these, the development is frequently unequal 

 on either side of a valley, and that the preponderance of the 

 deposit on the same (f. i. the westerly) side can sometimes be 

 observed in each, basin throughout a larger region. The lowest 

 portion of the surface of larger basins is frequently taken up by 

 stratified soil consisting of the finest particles of Loess, and ex- 

 hibiting a strong impregnation with alkaline salts. Over table lands 

 and plains Loess is spread in the shape of most uniform sheets. 



5th, The composition of pure Loess, which is the same from 

 whatever region specimens may be taken, extremely fine particles 

 of hydrated silicate of alumina being the largely pi-evailing in- 

 gredient, while there is always present an admixture of small 

 grains of quartz and fine laminte of mica. It contains, besides, 

 carbonate of lime, the segregation of which gives origin to the well- 

 known concretions common to all deposits of Loess, and is always 

 impregnated with alkaline salts. A yellow colouring matter caused 

 by a ferruginous substance is never wanting. 



6th. The almost exclusive occurrence of angular grains of quartz 

 in the pure kinds of Loess. 



7th. The complete absence of stratification. To this must be 

 added the singular position of the laminae of mica. When these 

 are deposited by water, they are arranged horizontally and ac- 

 cumulated in separate layers, while in Loess they are distributed 

 without any order, and occur in every possible position, 



8th. The capillary structure caused by the occurrence of innumer- 

 able tubes, mostly incrustated with carbonate of lime, which have 

 generally a vertical position, and ramify downwards like the roots 

 of grass. Where Loess is covered by vegetation, the tubes may be 

 seen taken up by rootlets to the depth of a foot or a few feet 

 from the surface. In this internal structure, besides the mode of 

 occurrence, is founded the chief difference of Loess from ordinary 

 loam. The former may be designated as a kind of calcai'eous loam 

 provided with internal structure. 



9th. The tendency to vertical cleavage, which, is the immediate 

 consequence of the two last-named properties. 



10th. The fact that land shells are imbedded in immense numbers 

 throughout the Loess, and that the most delicate shells are perfectly 

 preserved. Fresh-water shells are of extremely rare occurrence, as 

 has been correctly pointed out by Mr, Howorth. 



11th. The great quantity of bones of mammals found in the Loess, 

 the genera and mostly the species, or the next relatives, of which 

 are known to abound at present in steppes and on grassy plains. 

 Herbivorous animals are represented as well as carnivorous preying 

 on the former. 



12th, The fact that wherever Loess fills a basin between hills, 

 the inclined slopes of these are covered by angular fragments of the 

 adjoining rock, on which the yellow soil rests. Layers of these 

 fragments, beginning with a slight inclination and then passing into 



