CAMBEIAN AND LOWER ORDOVICIAN. 



Walcott's published section ^^^'^ (condensed) is as follows: 

 Section of Cambrian rocks in House Range, Utah. 



107 



Regarding the Pioche shale, Walcott *^'"' states : 



ThicTcness. — ^At Pioche, Nev., 210 feet. On the west face of the Highland Eange, 18 miles 

 west of Pioche, this formation is 170 feet thick. In the Eureka district of Nevada, 135 miles 

 northwest of Pioche, this formation lies between the Prospect Mountain quartzitic sandstone 

 and the great limestone series and is about 200 feet in thickness. In the House Range section, 

 105 miles north-northeast of Pioche, the formation is 125 feet thick. In the Big Cottonwood 

 section of the Wasatch Range, about 125 miles northeast of the House Range, near the old 

 shore line, the Pioche formation is represented by the lower portion of the arenaceous shales 

 which are here 250 feet in tliickness. The Pioche formation horizon is next met with to the 

 north where the line of the Canadian Pacific Railroad crosses the Contiaental Divide. At this 

 place the formation is called the Mount Whyte formation. 



K 18. PENNSYLVANIA. 



The results reached by Stose in the study of the Chambersburg quadrangle, 

 Pennsylvania, comprising part of South Mountain and the valley about Chambers- 

 burg, may be taken as representative for southeastern Pennsylvania. The follow- 

 ing statement *'"' is taken from an article in the Journal of Geology : 



The rocks in this area are largely concealed by the sandstone debris which covers the 

 mountain tops as well as the valleys and slopes. Their character, thickness, and relation are 

 therefore not readily determined. The structure is also compHcated by schistosity and jointing 

 which exist in all these rocks. The mountains are composed of Georgian (Lower Cambrian) 

 quartzites, sandstones, and shales and older igneous rocks; the adjacent portions of the valley 

 of Cambrian and Ordovician limestones and shales. 



Old volcanics. — The basement rocks exposed in the area are ancient volcanic rocks, green- 

 stone and altered rhyolite, which underlie the basal Cambrian imconformably. They occupy 

 the plateau-like tract overlooked by higher peaks in the center of the moimtain area sho^vn on 

 the map and in the extreme southeast corner and are extensively developed to the eastward. 



