402 



University of California Publications in Geology [Vol. 10 



of delta building. The frequent and irregular interbeddimg of coarse sands, 

 sandy clays and clays, the cross-stratified beds, the ripple-marked and sun- 

 cracked mud surfaces, the channels scoured by transitory streams, all prove the 

 abundance of sediments, the shifting conditions of deposition, the irregularity 

 of currents, the wide expanse of tide-flats and shallow waters and the weakness 

 of the waves. 



The admixture of flue and coarse material and the frequent alter- 

 nations in the series at Colfax conform very well to this general type 

 of delta deposits. Cross-bedding was, however, not observed in these 

 rocks, and other evidences of current action even in the less coarse 

 sediments are not at all apparent. 



Glacial 



The consolidated debris transported by glacial agencies has been 

 termed "tillite" by Professor Penek. Glacial deposits are character- 

 istically heterogeneous aggregates of finer and coarser material, com- 

 pacted but wholly unsorted. The matrix of the coarser phases usually 

 consists of angular grains of minerals and rocks, fresh feldspar and 

 quartz in very finely divided particles being especially abundant. 

 The individual grains of the matrix are commonly partly rounded and 

 partly angular. The coarser pebbles and boulders are generally 

 locally derived, but considerable proportions may come from distant 

 sources. Within a tillite, little if any assortment is to be expected; 

 masses up to several tons in weight may repose in an argillaceous 

 matrix. The shape of the pebbles in a glacial deposit is of great 

 diagnostic significance. Such ice-borne fragments are faceted occa- 

 sionally and sometimes have their edges rounded and ends snubbed. 

 The surface of at least a few of the pebbles is sure to be polished and 

 striated, with the majority of the striae paralleling the long axis of 

 the stone. Tillites are usually not bedded, although some may show 

 an obscure stratification ; sometimes pockets, lenses, and beds of coarser 

 and finer false-bedded material may be included in the unstratified 

 mass. 



Such deposits as above described are due to the deposition of 

 material as moraines, eskers and kames, but. other types of glacial 

 deposits are known. Thus in glacial-fed streams a well differentiated 

 type of deposit results which may here be termed fluvo-glacial ; all 

 gradations from typical tillite to well-marked fluviatile deposits may 

 be anticipated in such a deposit. In the case of a glacier directly 

 facing the sea, the reworked till may be sorted and well-bedded and 



