C. D. Walcott — Cambrian Bocks of Pennsylvania. 481 



to have the Huronian mass rising to view in the South 

 Mountains of the Atlantic States." 



I think that the view of Messrs. Frazer and Lesley that such 

 great thicknesses of strata occur in South Mountain arises 

 from the fact that these " great thicknesses " are but repeti- 

 tions of both the Cambrian and pre-Cambrian strata from 

 foldings and overthrust faultings and also from their not dif- 

 ferentiating between the cleaved schistose eruptives of the 

 Algonkian and the bedded and often cleaved sedimentaries of 

 the lower Paleozoic. 



The section at Monterey and along that portion of the Blue 

 Ridge is roughly, as estimated from the data obtained by Mr. 

 Keith to the south and from the Monterey section, reading 

 from below upwards, as follows: 



Feet. 



1. Shales , and slates, well shown near Mechanicstown, 



Maryland, and in numerous sections along the Blue 

 Ridge . . 300 feet to 400 



2. Coarse-grained and bluish-gray quartzite 1000 to 1200 



At several localities the shales of (1) appear to be 

 replaced by bands of conglomerate and shale ; and many 

 of the layers of (2) are conglomeritic to a greater or less 

 extent. 



3. Sandy shale, with interbedded layers of quartzite. 800 



4. Scolithus quartzite, with interbedded calcareous sand- 



stones and shales 500 



Fossils: — Camerella minor, and fragments of Ole- 

 nellus. 



5. Sandy shales, with a series of calcareous quartzite near 



the summit; about 450 



Fossils: — Camerella minor, Hyolithes communis, 

 and fragments of Olenellus. 



6. Mottled limestone, with intercalated sandy and shaly 



layers 800 to 1000 



Fossils: — Kutorgina n. sp., and fragments of Ole- 

 nellus 



This portion of the section is succeeded by the valley 

 limestone, more or less of the lower portion of which is 

 probably of middle and upper Cambrian age. 



The section includes from 3,000 feet to 3,500 feet of sand- 

 stones and shales before reaching the limestones. In a number 

 of localities a conglomerate was observed in the Lower sand- 

 stone series, in which fragments of the pre-Paleozoic crystalline 

 rocks were imbedded. This phenomenon was observed on 

 South Mountain, in the conglomerates mentioned by Prof. 

 Lesley, and also along the Blue Ridge and the Cotoctin ridge 

 to Harper's Ferry ; the conglomerate character of the rock 



