94 abstracts: geology 



the northeast. The rocks of the Valclez group overlie those of the 

 Orca group, as the result of a great overthrust fault. In the almost 

 complete absence of fossils the age of the various formations has not 

 been conclusively determined. 



The sulphide ore veins of the district, most of which are mined chiefly 

 for their copper content, but one of which is now producing gold ores, 

 occur in zones of fracture and shearing along fault planes. Most of 

 the mines and prospects occur in the greenstones, but the largest mine 

 is in slate and graywacke, stratigraphically beneath the greenstone. 

 The shear zones in many places are particularly well developed in slates 

 and graywackes interbedded with the greenstones, as these sedimentary 

 beds yielded to the deformational stresses more readily than the green- 

 stones themselves. The ores are, in part at least, replacements of the 

 crushed rock, but in the largest mine they are believed to replace cal- 

 careous sedimentary beds. The copper in the veins as well as the 

 gold is believed to be genetically connected with granitic intrusives 

 and not derived from the greenstones as has been previously suggested. 



S. R. C. 



GEOLOGY. — Rhode Island coal. George H. Ashley. U. S. Geo- 

 logical Survey Bulletin No. 615. Pp. 62, 5 plates. 1915. 



Coal occurs at a number of places near Providence and Newport, 

 Rhode Island. Attempts to use it as fuel began nearly 150 years ago, 

 but in spite of its favorable situation as regards markets and trans- 

 portation these have not met with success. 



The rocks of the Rhode Island coal field have been subjected to in- 

 tense lateral pressure which folded them in great folds with accom- 

 panying crushing, squeezing, and shearing. As in regions of intense 

 pressure and folding the softer rocks tend to yield, flowing away from 

 points of greatest pressure, so the Rhode Island coal has moved under 

 pressure and accumulated as irregular lenses in places of less pressure. 

 The pressure and accompanying heat changed the coal to anthracite 

 containing a high percentage of fixed carbon, and in places to graphite. 

 The graphite is localized where the metamorphism was greatest. In 

 general, the thinner the coal at any point, the larger the percentage 

 of graphite it contains. 



Crevices in the coal have locally become filled with quartz or 

 asbestos. 



The breaking open and recementing of the coal appears to have let 

 into it more or less of th?> adjoining shale, so that where the coal is 



