1885.] 6 J.) |Frazer. 



of this contact in Chester county north of the valley of that name, and in 

 all of them the quartzite lies " uncomformably " (*. e., with changed dip) 

 upon the schists. The latter, it is true, are somewhat different in minor 

 characteristics from those of which it is here the question, but so also is the 

 quartzite. Yet we have the best reasons for believing that each is of con- 

 temporary origin with its analogue in York county ; and indeed, the dif- 

 ferences, which would not be considered at all important by any but a 

 critical geologist, are what we might expect when we remember that these 

 rocks are sediments laid down at the bottom of successive seas, and that 

 their characters depended upon the kind of material which different 

 streams draining different parts of the country brought down to be strewn 

 out at different localities during different epochs.* 



It will be explained before long that the physical break between the 

 Archaean schists and the limestone series is rendered highly probable by the 

 observations in York county, but that between the flat arch belt and the 

 Hellam township quartzite must rest upon the direct evidence obtained 

 in other counties, unless here also we may apply the indirect method 

 mentioned above, and conclude that inasmuch as the Hellam quartzite 

 contains one important fossil (Scolithus linearis) and the Archaean schists 

 contain none that have yet been discovered in York county, this fact 

 alone entitles them to be considered different formations. 



The Hellam or Chikis quartzite is a hard quartzose rock, of which the 

 general color is white or gray, tinted by some other color, usually pink, 

 brown or blue, depending upon the minerals with which it has been asso- 

 ciated. It is almost always crystalline, and in disturbed regions like this is 

 most frequently found in broken fragments rather than in continuous beds. 

 This is probably owing to its brittleness, which prevented it from yield- 

 ing gradually to the strain which has folded and tilted the other rocks of 

 the county. These strains have twisted, broken and crumbled it, but on 

 account of its great hardness and its resistance to the chemical action of 

 the atmosphere, it is the least altered or decomposed of all the rocks to 

 be considered here, and almost always indicates its presence by a hill, 

 whatever be the position of its strata, f 



It is not necessary to specify the localities within the county where this 

 quartzite occurs, because they are indicated by brown on the accompany- 

 ing geological map ; still less is it desirable to discuss here all the possi- 

 bilities of structure which these scattered outcrops suggest. It is important, 

 however, before leaving the floor of the Palaeozoic column, to say that 

 eleven years of experience in the field have caused me to doubt the cor- 



* Let any one observe the great differences between the characters of the sand 

 beach of our own Atlantic coast within short distances. See on this subject 

 Delesse's important contribution entitled " Geologie du fond des niers," and 

 tbe writer's notice of the same in the Proc. Am. Philos. Soc. 



t Of course the reason of this is that the erosion, which has torn off hundreds 

 and perhaps thousands of feet of the other measures, has not been able to 

 reduce it to the same extent, and itremains, consequently, as an elevation, or 

 chain of hills. 



