SEDIMENTARY ROCKS 



201 



thickness of the conglomerate, rather favors the glacier theory. Thus, 

 until more evidence has been obtained,' the origin of this conglomerate 

 must remain an open question. 



This conglomerate overlies the Devono-Cambrian limestone-dolomite 

 beds and appears also to overlie the Carboniferous shales and cherts, but 

 of this the evidence is not conclusive. The conglomerate was thus prob- 

 ably formed about Carboniferous time, and may correspond to the Permo- 

 Carboniferous tillites or conglomerates, considered to be of glacial origin, 

 that occur in South Africa, Australia, India, and other parts of the 

 world.*® 



Mesozoic-Pennsylvanian — Orange group. — The members of the Orange 

 group are the most extensively developed rocks along the 141st meridian 

 between Yukon and Porcupine rivers. The most northerly exposure of 

 these beds within this belt occurs about 13 miles south of the Porcupine, 

 and thence they occur more or less persistently to Yukon Elver. Within 

 the portion of this distance from Eat Creek, at about latitude ^^° 45', 

 to 3 miles south of Ettrain Creek, at latitude approximately 66° 23', a 

 distance of about 95 miles, the beds constitute the prevailing rock ex- 

 posures. 



This group of rocks consists chiefly of shales, sandstones, conglomerates, 

 slates, phyllites and quartzites, but also includes occasional beds of lime- 

 stone which contain Upper Carboniferous fossils, and are limited to the 

 lower portion of the formation. All gradations occur from only slightly 

 altered shales and sandstones to much metamorphosed slates, phyllites, 

 and quartzites; in fact, almost every type and variety of normal argilla- 

 ceous and arenaceous sediment is represented, and all are so intimately 

 associated and pass so gradually from one phase to another that in the 

 field it was found necessary to consider them all as a geological unit. 



On account of the general paucity of outcrops and owing also to the 

 metamorphosed condition of the beds in places, no complete section of the 

 Orange group was measured at any one point, although partial sections 

 were measured in several places. Also nowhere was any consolidated 

 geological formation found overlying these rocks, so that it is uncertain 

 whether or not the uppermost member of this group was seen. Conse- 

 quently it is not at all definitely known what aggregate thickness the 

 beds have, but the group is at least 6,000 feet thick and may be nearer 

 twice this amount. 



^ A. P. Coleman : Glacial periods and their bearing on geological theory. Bull. Geol. 

 Soc. Am., vol. 19, 1908, pp. 349-353. 



E*. H. Hatch and G. S. Corstorphine : The geology of South Africa. London, 1905, 

 pp. 199-210. 



A. W. Rogers : An introduction to the geology of Cape Colony. 1905, pp. 147-179. 



XIV — Bull. Gbol. Soc. Am., Vol. 25, 1913 



