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CAPE COD GEOLOGY 



iferous pebbles were carried to the region extending from Newport nearly to 

 North Atterbury. Along with the Cambrian pebbles were a few that carried 

 marine Devonian fossils. Pebbles of both these types were dragged out of ledges 

 of conglomerate at Taunton and Newport during the glacial epoch and carried 

 southward to Block Island and M'arthas Vineyard. 



While Carboniferous sediments were being laid down, bodies of granitic 

 magma were intruded along the west side of the site of Narragansett Bay, con- 

 verting sandstone and shale into gneiss and schist and forming new minerals. 

 Abundant fragments of these rocks are found in the drift on Block Island. 

 Farther north, about North Attleboro and near Boston, basic igneous rocks, in 

 the form of dikes and sills, as well as lava flows, formed melaphyre, diabase, and 

 other dark, heavy, iron-bearing rock, fragments of which occur in the drift in the 

 region on the south. Among these igneous rocks were large quantities of an acid 

 lava, the felsite or apo-rhyolite seen in North Attleboro and about Boston 

 and Salem, fragments of which are found from Cape Cod and Nantucket west- 

 ward to Block Island. Hot springs that accompanied this igneous action formed 

 large masses of quartz, in stocks and in veins, as at Diamond Hill, Rhode Island, 

 fragments of which are found in the glacial drift farther south. A few miles west 

 of Diamond Hill there is a mass of an ancient eruptive rock, periodotite, rich in 

 iron, fragments of which are scattered from Gay Head to Block Island. 



By the end of the Carboniferous period the coal beds were thrown into 

 mountainous folds that form what Shaler termed the East Appalachians. This 

 mountain range probably embraced the site of Cape Cod and the neighboring 

 islands. The height of this range above sea level at Canton Junction was prob- 

 ably 15,000 feet. This mass of rock, of which little or no trace here remains, 

 appears to have been worn down nearly to the present level of the lowland of 

 eastern Massachusetts by the end of the Cretaceous period. 



During Cretaceous time weathering and erosion along the site of the present 

 south coast of New England produced a surface of slight relief, over which streams 

 carried sand and clay southward toward the Atlantic, which then lay at an 

 unknown distance beyond the present islands. Thus was built up a plain like 

 that now seen along the seaboard south of New York, on which from time to 

 time the trees and shrubs of late Cretaceous time were buried in the low places 

 and lagoons in which they grew, forming the lignite now found. Before the end 

 of the Cretaceous period the sea came in upon the land, extending far inland. 



Between the end of the Cretaceous period and the beginning of Miocene 

 deposition here there was a long period of erosion, probably more than one 



