Geology and Mineralogy. 389 



in the eastern part of the United States was affected at this time, 

 extending from the St. Lawrence to Alabama. Sediments which 

 had been accumulating for ages were forced into smaller com- 

 pass. Along the present Appalachians the rocks were folded into 

 arches ; and the more severe compression in New England resulted 

 in profound alteration of the rocks and the production of slates, 

 schists, and gneisses. The result is that no unchanged sediments 

 of pre-Triassic age exist in Connecticut, but their metamorphosed 

 equivalents are present everywhere. The igneous intrusions have 

 likewise been forced in many places to develop schistosity and to 

 take on gneissoid structure." 



The geological formations of the metamorphic areas which 

 have resulted from this geologic history include those of the 

 Western and Eastern Highlands. In regard to the former it is 

 stated that — 



"With the exception of a small area of Triassic rocks in 

 Woodbury and Southbury, the entire western part of Connecti- 

 cut, bounded by a line extending from New Haven to North 

 Granby, is composed of ancient crystalline rocks. The distinct 

 formations here represented are — the Becket gneiss, which is 

 regarded as a pre-Cambrian complex equivalent to the Fordham 

 gneiss in the vicinity of New York City ; the Poughquag quartz- 

 ite, of Cambrian age ; the Stockbridge limestone of Cambro- 

 Ordovician age ; the Berkshire (Hudson) schist, of Upper 

 Ordovician age ; and the Hartland (Hoosac) schist, probably of 

 Silurian age. The Waterbury gneiss is Hartland schist modified 

 by igneous injections. In addition to these there are igneous 

 masses ; namely, the Danbury granodiorite-gneiss, Brookfield dio- 

 rite, Thomaston granite-gneiss, Collinsville granite-gneiss, Bristol 

 granite-gneiss, Prospect porphyritic gneiss, Litchfield norite, areas 

 of peridotite, and numerous amphibolite dikes and pegmatite 

 veins. In the southeastern part of the district are found the 

 Orange phyllite and the Milford chlorite schist." 



The relations as regards the Eastern Highlands are summarized 

 as follows : 



" All of the state of Connecticut east of a line extending from 

 Lighthouse Point, New Haven, to Somers, is made up of ancient 

 crystalline rocks, nearly all of which have been affected by 

 intense regional metamorphism. The formations in this section 

 of the state have not been so carefully studied as those west of 

 the Triassic area, and many of the statements regarding them 

 are to be considered preliminary and subject to radical revision. 

 In some cases the boundaries of the formations have been of 

 necessity arbitrarily drawn, because the rocks seem to grade into 

 one another, and yet to present such differences as to make it 

 worth while to give them separate names. 



"The geological formations occurring in the Eastern Highland 

 may be summarized as follows : — The Monson and Branford 



Am. Joxjr. Sci.— Fourth Series, Vol. XXIII, No. 137.— Mat, 1907. 



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