334 Scientific Geology. 



fore been regarded, either as graywacke slate, or talcose slate, or both.* 

 But after a careful examination of this formation in various places, 

 from the mouth of the Merrimack to Connecticut line, I am con- 

 strained to regard it as one of the latest varieties of mica slate : prob- 

 ably what Humboldt would call transition mica slate. True, I have oc- 

 casionally met with a limited portion-of this rock, which had somewhat 

 of a mechanical aspect : though not much more so than I have found 

 in every range of mica slate which I have examined. In some cases 

 too, there exists a glazing, apparently talcose, on the laminae of the 

 rock ; and this variety certainly approximates closely to graywacke 

 slate. Still, these are not the predominant characters of the formation. 

 Generally the rock is composed of gray arenaceous quartz, and mica 

 in minute scales : the rock exhibiting too much of a crystalline struc- 

 ture for graywacke, and containing, moreover, but little if any argilla- 

 ceous matter. Where it contains a considerable oxide of iron, as in 

 the northeast part of Worcester, it presents at a little distance the dirty 

 appearance of sandstone : but a closer examination will show the 

 characters above pointed out. I saw not the least trace, moreover, of 

 any organic remains in this formation; nor have I any evidence that 

 such have ever been found. In short,though very probably genuine cab- 

 inet specimens of graywacke slate may be found in this formation, yet 

 as a whole, I could not, without doing violence to my convictions, refer 

 it to any formation but mica slate. But as I shall place quite a num- 

 ber of specimens from this formation in the hands of the Government, 

 others by inspecting them can form their own opinions as to their 

 nature. 



I ought to remark that quartz very frequently predominates in this 

 formation, and the mica almost disappears. Indeed, I am by no means 

 sure that quartz is not the predominant ingredient in the whole for- 

 mation : and if so, it ought to be denominated quartz rock. And it 

 seems to me that there is much more reason to doubt as to this point, 

 than whether it ought to be referred to graywacke, or talcose slate. 



As we approach the east and west sides of this range, the charac- 

 ters of the mica slate become more decided ; and in this slate of ap- 

 parently greater antiquity, the veins and protruding masses of gran- 

 ite are more numerous ; though they occur in every part of the for- 

 mation, and sometimes in the argillaceous slate connected with it. 

 Except that in Worcester, Fitchburg, and Pelham, (N. H.) no at- 



* Eaton's Canal Rocks and Geological Text Book. 



