C. D. Waleott — Cambrian Rocks of Pennsylvania. 37 



America, and that we have them all in Eastern Pennsylvania, 

 we can conclude that the total time from beginning to end 

 was small, and of so recent a date that the streams — though 

 resting on beds of clays — -have not not reached in all cases their 

 pre-glacial bottoms, and the exposed rocks — in spite of greater 

 or less exposure to the atmospheric agencies — have not had 

 time to acquire signs of decomposition or even oxidation. In 

 fine, we seem to have had but one ice age, and that a short and 

 recent one. 



Art. IV. — Notes on the Cambrian Rocks of Pennsylvania, 

 from the Susquehanna to the Delaioare • by Charles D. 

 Walcott. 



In a former paper a report was made of an examination of 

 the lower Paleozoic rocks,* from the Susquehanna to the Poto- 

 mac, and now attention is called to some observations, made 

 during the past field season, relating to the basal quartzites and 

 limestones of the lower Paleozoic rocks that extend across 

 Pennsylvania, from the Susquehanna river to the Delaware 

 river and across New Jersey to Orange county, 'New York, on 

 the north, and into Chester county, Pennsylvania, on the east. 



In the paper mentioned it is stated that Hyolithes communis 

 and fragments of Olenellus were recognized in the material 

 collected from limestones in Lancaster county, on the east side 

 of the Susquehanna river,f and that, from the closely related 

 stratigraphic arrangement of the rocks of Lancaster county, it 

 is probable that all the Lancaster limestones will fall within 

 the Cambrian, unless it be that some portion of the upper 

 series may pass into the Ordovician. This generalization will 

 also apply to the limestone in the adjoining counties of Berks 

 and Chester, and, in fact, to the entire extension of this series 

 northeastward, to the Delaware. All of the quartzites that 

 have been referred to the Potsdam will necessarily fall into 

 the lower Cambrian, as they are beneath the limestones.^ 



Prof. A. Wanner, of York, Pa., accompanied me in the ex- 

 amination of the limestones about the city of Lancaster. His 

 familiarity with the positions of the quarries and natural out- 

 crops enabled us to make a rapid examination of the limestones 

 along Conestoga creek, and, although no fossils were found, I 

 saw no reason to think that the limestones were not of Cam- 



* Notes on the Cambrian rocks of Pennsylvania and Maryland, from the Sus- 

 quehanna to the Potomac, this Journal, vol. xliv, 1892, p. 469. 

 fLoc. cit , p. 474. 

 % Loc. cit , p. 475. 



