320 



Scientific Geology. 



of Macculloch.* Ths size of the imbedded pebbles is usually about 

 an inch. It greatly resembles the rock that constitutes the first ridge 

 of the mountain range on the east side of Wyoming valley, in Wilks- 

 barre, Pennsylvania ; and which there probably underlies the the an- 

 thracite coal formation. 



This rock being most decidedly mechanical in its texture, will 

 throw some light on the age of the quartz rock, and associated lime- 

 stone of Berkshire valley, if it be admitted that it forms a part of the 

 series ; of which I think there can be but little doubt. 



It will be perceived that the varieties, Nos. 5, 6, and 8, above de- 

 scribed, are different from any mentioned by Dr. Macculloch, and so 

 far as I know, by any writer. 



In order to have a complete view of quartz rock, as it exists in 

 Massachusetts, we ought to recollect that two varieties (red and blue,) 

 have already been described as comprehended in the graywacke for- 

 mation. 



Topography of Quartz Rock. 



On the map I have represented all the quartz rock in the State (ex- 

 cept that connected with the graywacke,) as associated with mica 

 slate, talcose slate, or gneiss. It is also more or less connected with 

 other rocks ; as with limestone in Berkshire, and with argillaceous 

 slate in Bernardston. But in all other cases, except in regard to 

 gneiss and mica slate, it is little more than a juxtaposition of the two 

 rocks ; whereas the quartz rock alternates with, and passes impercep- 

 tibly into gneiss and mica slate. And in fact it might be regarded 

 very properly as a member of the gneiss and mica slate formations. 



In Cumberland, Rhode Island, I have marked a strip of quartz 

 rock as connected with the peculiar rock that prevails in that place, 

 and which I venture to denominate talco-chloritic slate ; although its 

 characters are very obscure. Or rather the quartz rock lies between 

 this slate and the graywacke on the east ; and I think also that it al- 

 ternates with the talco-chloritic slate. In the northeast part of the 

 town, it forms a hill of considerable altitude, of snowy whiteness. 

 More westerly its color is gray, and it is of a coarser texture. 



I take this opportunity to remark, that I do not feel confident that 

 even on the second edition of the geological map, and after a re-exami- 

 nation of that region, I have correctly delineated the rocks of Cum- 



* Geological Translations, vol. 1. p. 60. Second Series. 



