808 



THE EEGOLITH 



composed of an indiscriminate admixture of particles of all 

 sizes, from those as fine as dust to blocks it may be of hundreds 

 of tons' weight Such are necessarily limited to the immediate 

 vicinity of the cliffs or mountains from which they are derived. 

 As loosened by heat or frost from the parent masses, the frag- 

 ments tumble down the slopes, gradually accumulating in beds 

 the inclination of which is limited only by the laws of 

 '■•^ gravity and the character of the debris (See PL 25.) 

 •; Inclinations of 30° are common. From their 



""^-- mode of origin it is natural that the individ- 

 \ ual particles should be mainly angular and 

 \ comparatively fresh. In fact, they represent 

 \ rock- weathering through disintegration, and 

 not decomposition, which will come later. 

 Above, they consist simply of masses of 

 loose rock wholly unfitted for the support 

 of vegetable life ; below, they pass gradu- 



Soil hearing pc^ti/oru 



^afXless partftaiv 



Fig. 31. — Diagram 

 showing the history 

 of a talus, a, bed 

 rock; hh, talus; c, de- 

 stroyed portion of a eliff, 

 the material being now in 

 the talus. 



ally into soils. (Fig. 31.) 

 Through becoming saturated with 



water, ice, or snow, such at times become loosened from 

 the steep slopes on which they lie and slide down in the form of 

 avalanches into the valleys. (PL 27.) Although comparatively 

 limited in their extent, these latter, owing to the resistless 

 energy and suddenness of their advance, are sometimes appall- 

 ingly destructive, as has been repeatedly illustrated in mountain 

 regions the world over. The geographic distribution of talus 

 deposits as controlled by climatic conditions has been already 

 noted, 



(2) Alluvial Deposits. — The deposits included under this 

 head differ structurally from those thus far described in that 

 they are always more or less distinctly stratified, or bedded. 

 In writing of the formation of sedimentary rocks, and again 



