292 



THE EEGOLITH 



made by Messrs. Chamberlin and Salisbury: *^ Above, the 

 clay graduates into soil which, outside the valleys, is uniformly 

 shallow. Beneath the soil, the clay loses the dark color of the 

 latter, due to the presence of organic matter, but is for a certain 

 distance downward not unlike the superior portion in texture. 

 The deeper lying clay, where limestone is the subjacent rock, 

 is the most characteristic member of the residuary earth series. 

 It is not like that above, structureless, although, like that, it is 

 without trace of stratification. It generally shows a tendency to 

 cleave, breaking up into little pieces which are roughly cubical. 

 This is often conspicuous, and especially so on the faces of 



sections which are thor- 

 oughly dry. In such situ- 

 ations large quantities 

 of the clay in small angu- 

 lar blocks may be removed 

 by slight friction. The 

 size of the cuboids varies, 

 within somewhat narrow 

 limits, from a small frac- 

 tion of an inch to one or 

 two inches in diameter. 

 This cleavage is probably 

 a phenomenon of shrink- 

 age due to drying, as it 

 partially disappears when 

 the clay becomes wet. 

 This structure has given 

 rise to the local name of ^ joint' clay, an appellation not alto- 

 gether inappropriate, 



**Upon drying, this variety becomes very hard and rock-like. 

 It only becomes adapted to serve as soil by surface amelioration, 

 as is shown by the fact that, from the thousands of mineral holes 

 scattered over the southern part of the mining district, the 

 material ejected still lies beside the excavations as heaps of clay, 

 without covering of vegetation, although it has been exposed in 

 most cases for many years. Notwithstanding this fact, the 

 clay, even in its deepest parts, wherever examined, is found to 

 abound in minute perforations. These, in many cases at least, 

 indicate the penetration of rootlets, for the rootlets themselves 



Pig. 28. — Showing angular character of 

 quartz particles in decomposed gneiss. 



