470 CD. Walcott — Cambrian Mocks of Pennsylvania. 



named by Frazer) and equivalent to the upper Cambrian 

 quartzite of Walcott. He prefers to use the older name 

 u Chiques " for these sandstones, stating that it is best to get 

 rid of the old name "Potsdam" sandstone, as there does not 

 seem to be any satisfactory evidence that the proper Potsdam 

 sandstones of the Canada line and Lake Champlain extended 

 as far south as southern Pennsylvania. He says that the sec- 

 tion at " Chiques Rock " is not quite comprehensible at one or 

 two points. I found that it was so complicated by thrust 

 faulting that it is not a typical section. It exposes, however, 

 the lowest of the Cambrian rocks now known to me in central 

 Pennsylvania. The " Chiques Pock " proper, near Chiques, is 

 the Scolithus quartzite, and is in an unbroken section at the 

 summit of the series of the quartzites and slates of the Chiques 

 section although now apparently at the base of the section. 

 The quartzites to the south, between " Chiques Rock " and the 

 limestones at Columbia, are older and have been raised up 

 from beneath and thrust over on the Scolithus quartzite at 

 " Chiques Rock." This is determined by the succession shown? 

 in the section exposed on the flanks of South Mountain, in 

 Franklin county west of Monterey, reference to which is made 

 in the notes on the geology of South Mountain. In relation to 

 the stratigraphic position of the slates, etc., beneath the Lan- 

 caster limestone, I will quote the statement of Professor 

 Lesley, " The geographical proof that the slates overlie the 

 quartzite is complete ; and establishes the correctness of Pro- 

 fessor Rogers' Upper Primal slate formation. The geological 

 evidence is equally conclusive ; for the general dip in the- 

 Chiques rock is southward, under the slates ; and of the slates 

 southward under the limestone."* 



The continuation of " Chiques Rock " to the westward, in 

 York county, forms the Hellam hills f and shows a broad anti- 

 clinal of quartzite surrounded by schists. Numerous sections 

 along the southern and western sides of the Hellam hills show 

 that the quartzites pass beneath a series of shales, slates, sandy 

 and calcareous layers that, in turn, pass beneath the limestones 

 of the valley. 



It was my good fortune to have the acquaintance of 

 Prof. A. Wanner, superintendent of public schools at York. 

 He volunteered to be my guide to localities where there 

 were good exposures of the quartzites, schists and limestones, 

 and he gave me valuable assistance. A reconnaissance was 

 first made of the section at " Chiques Rock " south to Colum- 



*Loc. cit.; p. 1?2. 



f I did not learn of any local name for this ridge of hills when in York county, 

 and as most of the ridge is within the township of Hellam I shall speak of them 

 as the Hellam hills. 



