Page:The Journal of geology (IA journalofgeology11893univers).pdf/360
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 regarding the area, notwithstanding the limited facilities and unsatisfactory 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 sometimes 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, continued north from the ridge bounding the valley at Weed's Quarry (Kl.) on