ABSTRACTS 



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GEOLOGY. — The gabbros and associated rocks at Preston, Connecticut. 

 G. F. Loughlin. Bulletin U. S. Geological Survey No. 492. 1912. 

 Pp. 158, with maps and sections. 



The Preston region, a quadrangular area of about 102 square miles, 

 lies in the southeastern part of Connecticut, a few miles north of Ston- 

 ington on Long Island Sound. The pre-glacial formations comprise 

 metamorphic sedimentary rocks, gabbro and granite intrusions, and an 

 immense mass of quartz. The metamorphic sedimentary rocks, as- 

 signed provisionally to the Cambrian and Carboniferous, include quart- 

 zite, quartz-biotite schist, hornblende schist, black pseudoporphyritic 

 schist (kinzigite), and dolomite, all, so far as local evidence shows, con- 

 formable. The gabbro, comprising two principal and several minor 

 varieties, forms a main mass of oval outline, a few outliers, and some in- 

 trusive sheets. The granite, comprising three varieties, is represented 

 by numerous intrusive sheets. 



In the schists derived from sedimentary rocks the schistosity, so far 

 as observed, is coincident with original bedding. Major folds are not 

 clearly marked, but overturned synclines are indicated in the eastern 

 and western parts of the area. During folding the central gabbro mass 

 acted, with respect to the schists, like a large resistant pebble in the 

 relatively plastic matrix of a mashed conglomerate. The secondary 

 strains induced by its deformation in conjunction with the primary 

 folding of the region, tended to develop abnormal crumpling locally and 

 were sufficient to determine the paths of the granite intrusions. The 

 intrusion of this granite completed the local deformation. 



Both the main mass and the outliers of the Preston gabbro appear 

 to be sills. Consideration of the effects of regional metamorphism indi- 



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