782 THE JOURNAL OF GEOLOGY. 



the structure within this tongue-like area, which includes 

 between twenty and twenty-five square miles. The field work 

 was mainly done in 1888, though the southern portion of the 

 area was revisited in 1891, when the writer was assisted by Mr. 

 Louis Kahlenberg, and again in 1892 when he was assisted by 

 Mr. H. J. Harris. The work has been in charge of Professor 

 Pumpelly, then the head of the Archean Division of the U. S. 

 Geological Survey. 



Views of Percival and Dana regarding the area. — Though the 

 map accompanying Percival's report does not indicate the schist 

 areas within the area which is under consideration, he several 

 times mentions them in the text. One is surprised to find how 

 accurate were his observations and how correct his views regard- 

 ing the area, notwithstanding the limited facilities and unsatis- 

 factory condition of his survey. The following extracts from 

 his report 1 contain the more important statements which he 

 made having reference to this area. 



" It (the limestone) is accompanied throughout with Mica Slate some- 

 times forming thin interposed beds, and at other times extensive ranges. The 

 Mica Slate, in the vicinity of the limestone, particularly when interposed in 

 thin layers in the beds of the latter, is very generally dark and plumbaginous, 

 but occasionally light gray, as in the more extended ranges. These latter 

 usually occupy high narrow abrupt ridges, sometimes quite isolated, and at 

 other times in longer ranges, generally with an irregular outline." (Pp. 

 126-127). 



" A coarse dark Mica Slate, veined or knotted with quartz, and often 

 abounding in staurotides and garnets, occurs especially in the north part of 

 the ridge bounding, on the west, the valley south of Lime Rock village, 



" (P. 127)- 



" The general surface of the valley, in the north part of Salisbury, in 

 Canaan, and in the adjoining part of Massachusetts, is low and level, but 

 traversed by ridges of Mica Slate, often high and abrupt, either isolated, or 

 in long continuous ranges, the latter generally presenting a distinctly curved 

 outline." (P. 129). 



" Between these two branches 2 extends a series of Mica Slate ridges, con- 

 tinued north from the ridge bounding the valley at Weed's Quarry (Kl.) on 



1 Report on the Geology of Connecticut, by James G. Percival, New Haven, 

 1842, pp. 124-130. 



2 Of the Housatonic Valley. 



