January 24, 1896.] 



SGIENGE. 



143 



witMn the basin, aud the deposits of glacial 

 drift, chiefly water-laid, frequently approach a 

 hundred feet in thickness. 



The rocks enclosing the basin are mainly 

 gneisses, hornblende granites, and, on the west, 

 some quartzites. Exceptinga few of the gran- 

 ites, they are all Pre-Carbouiferous and extend 

 over wide areas of country. They have a south- 

 east-northwest trend, and the gneisses and 

 quartzites dip to the northeast, as seen in the 

 Manville section and at Woonsocket Hill. Com- 

 pared to the rocks within the basin, they are hard 

 and form good resisters to weathering. To this 

 difference of resistance to weathering between 

 the extra- and the intra-basin rocks, the basin 

 doubtless mainly owes its present topography. 



The rocks within the basin are soft, have a 

 southwest-northeast trend, and dip northwest. 

 They are much younger than the enclosing rocks, 

 with which they exhibit marked unconformities, 

 as with the quartzites on the west and the gneis- 

 ses on the north. The lowest and apparently 

 oldest of these rocks, but of unknown age, is a 

 uniformly very fine grained, grey, talcose, 

 silicious mica-schist, which in the past has been 

 worked with i^rofit in the whetstone industry. 

 It occurs chiefly in the southeast side of the 

 basin. Above this grey rock, but unconform- 

 able with it, in the west part of the basin, is 

 found a shiny black hornblende mica-schist, 

 also of questionable age ; while unconformably 

 over both the grey and the black lie the 

 youngest rocks in the basin. These latter, 

 though as yet they have yielded no fossils, are 

 probably Carboniferous, judging from their 

 geological relations and lithologic resemblance 

 to the well-known Carboniferous on the east, 

 in the Narragansett Basin. They consist of 

 grey conglomerates with interbedded mica- 

 schists, sandstones and slates. They are de- 

 rived chiefly from the surrounding older rocks 

 of the upland, as is manifest by the granite 

 and quartzite pebbles contained in the conglom- 

 erates, occurring east of Forestdale and at 

 Woonsocket Hill. 



Cutting the rocks in the basin at intervals is 

 a series of diabase dikes. They range from less 

 than one to more than a hundred feet in width, 

 dip about vertical, and run nearly parallel, 

 bearing north-northeast. ' 



Preliminary Report on the Stamford Gneiss : By 



W. H. Snydee. 



In the southwestern part of Vermont and ex- 

 tending into the northwestern part of Massa- 

 chusetts there occurs a coarse banded gneiss 

 .covering about 50 square miles and called by 

 the U. S. Geological Survey the Stamford Gneiss. 

 It was known in Pres. Hitchcock's survey of 

 Vermont as the Stamford Granite. 



This gneiss is surrounded on the east and 

 south by a metamorphosed conglomerate, the 

 pebbles of which correspond to the blue quartz 

 of the gneiss. At a short distance from the 

 contact the conglomerate changes into a mica- 

 ceous quartzite. In this quartzite there has 

 been found by Walcott trilobites which prove it 

 to be Cambrian. On the west the gneiss ap- 

 pears to be bounded by a very massive white 

 quartzite, the dip and strike of which mostly 

 correspond to that of the micaceous quartzite 

 on the east. The northern boundary is as yet 

 undetermined. 



At the contact of the conglomerate and gneiss 

 there is developed between the two a layer of 

 about a foot in thickness in which the gneissic 

 structure is particularly pronounced, the mica 

 making lenticular folds around the quartz grains 

 and giving the mass the appearance of augen- 

 gneiss. Prof. Pumpelly has suggested that this 

 layer is the disintegrated border of the gneiss 

 upon which the conglomerate was laid down 

 and which has since been metamorphosed. 



The gneiss itself is composed of coarse feld- 

 spar crystals, irregular masses of blue quartz 

 and thin layers of a greenish mica. In some 

 parts there are large Carlsbad twins of microcline 

 and in others rounded masses of feldspar 3 and 4 

 inches in diameter. At one point the weather- 

 ing has developed nodular feldspar aggregates 

 as large as a hen's egg, which give the face of 

 the ledge a conglomeratic appearance. The 

 rocks yield easily to weathering throughout 

 the area. There are no glacial strise apparent 

 upon any exposed surface. 



Near the western border of the gneiss there 

 is an outcrop of a fine grained greenish gneiss 

 very distinct from that of the main mass and 

 surrounded on three sides by this mass. The 

 fourth side is hidden by a bog. The Stam- 

 ford gneiss apparently overlies this gneiss and 



