374 The Loess of North America. [May. 



origin. Professor J. D. Whitney says of them 1 that they " have 

 been formed in the loess by infiltration along the lines of cleavage 

 and resultant chemical action on calcareous matter occurring in 

 large quantity along certain planes." 



It should be noted, in framing any theory on these peculiar 

 bodies, that zvithovt exception the fissures of the interior surface 

 end with the outer calcareous envelope, as shown in Plate V (Fig. 

 I and 2, c and a). So also should be considered the numerous 

 rugosities or protuberances more or less thickly studded over 

 their surfaces (Plate v, Fig. 3).- Further, there often occur, in 

 the pyramidal masses of the interior, numerous small black masses, 

 apparently carbonaceous, the true nature of which has not yet 

 been satisfactorily determined. I am, however, disposed to con- 

 sider these concretions as a result of chemical changes in the 

 composition of the loess itself through the action of carbonic 

 and various of the humus acids. These exert, as is well known, 

 a marked action upon certain mineral substances contained in 

 soils, as notably upon carbonate of lime. 3 Whether there may have 

 been an original foreign nucleus about which accretion began I 

 am unable to say, but the fact is, that in none of the above men- 

 tioned 2803 specimens could any such nucleus be found. 



On one other point the writer's observations lead to negative 

 results. In every case, even when from considerable depths, the 

 concretions are of a stojiy hardness. One observer 4 states that 

 " when first exposed, most of these concretions are soft enough 

 to be rubbed fine between the fingers, but they gradually harden 

 by being exposed to the atmosphere." Furthermore, the portion 

 interior to the outer calcareous envelope is largely, more than 

 one-half, carbonate of lime. A little more than one-third is silica, 

 with a small per centage of alumina. We have here, then, the 

 conditions which produce their hydraulic properties, a fact in it- 

 self sufficient, almost, to lead to a belief in their universal 

 hardness. 



Another feature of the loess remains to be noticed, which is in 

 some particulars its most remarkable characteristic. Reference is 



' American Naturalist, Vol xi, p. 709. 



Viiie Darwin's 

 , wonderful volt 

 Aughey, Sketcl 



