136 MORLEY E. WILSON 
the green or greenish-gray color which is everywhere characteristic 
of the conglomerate is not the color which usually distinguishes 
more recent fluviatile gravels developed in arid or semiarid regions, 
so that unless the pre-Cambrian atmosphere was deficient in oxygen 
this feature also points to humid climatic conditions. Fluviatile 
conglomerates of the coarse unsorted types which are characteristic 
of the Cobalt series are limited on the earth’s surface at present 
to regions of youthful topography or arid climates.* These 
factors, usually operating together, have resulted in the building 
up of immense accumulations of river gravels on piedmont slopes 
and in interior basins. If it be assumed, therefore, that the con- 
glomerates of the Cobalt series are of fluviatile origin, this conclu- 
sion must be reached in the face of the facts that these immense 
deposits covering a. minimum area of 20,000 square miles were 
built up in a region having a low relief and a pluvial climate, 
conditions which in every particular are the reverse of those under 
which similar fluviatile deposits are accumulating on the earth 
today. 
6. Glacial deposition —In a number of papers published within 
the last few years, A. P. Coleman has advocated the glacial origin 
of the conglomerates of the Cobalt series, pointing out their strik- 
ing similarity to the Pleistocene glacial deposits and to similar 
rocks in other parts of the world to which a glacial origin has been 
assigned. The principal features emphasized by Coleman are 
the resemblance of the matrix of the conglomerate to bowlder 
clay; the enormous extent and great thickness of the conglomerate; 
the occurrence of immense bowlders at a distance of several miles 
from the source of supply; the great size, angularity and variety 
of the pebbles and bowlders of the conglomerate; and, finally, the 
finding of scratched and “soled”? pebbles and bowlders in the 
conglomerate at Cobalt, Ont.? 
* Medlicott and Blanford, Geology of India, p. 397; Huntington, Carnegie Inst. 
Exploration in Turkestan, p. 40; J. Barrell, Jour. Geol., XIV (1906), 330; A. C. 
Trowbridge, ibid., XIX (1911), 738; E. W. Hilgarde, Sci., N.S., XV (1902), 414; 
N. S. Shaler, Ball. Geol. Soc. Amer., XII (1907), 271-300; I. C. Russell, Geol. Mag., 
VI (1886), 289-95; J. L. Rich, Jour. Sci., XVIIL (4910), 601-32. 
2 Amer. Jour. Sci., XXIII (1907), 187-92; Jour. Geol., XVI (1908), 149-58; Bull. 
Geol. Soc. Amer., XIX (1908), 347-466. 
