10 J. Bar r ell — Relations of Subjacent Igneous 



in 1911, in smaller areas adjacent to Narragansett Bay. 

 The Grreen Mountain granitic axis shows inclusions of 

 sediments corresponding to the Grenville series, and these 

 doubtless are an extension of the Laurentian granite 

 gneisses as sho\vn in Canada and the Adirondacks. The 

 indications are that the axis once formed the floor of 

 all New England upon which the Paleozoic sediments 

 were laid down. The character of the Laurentian 

 has been described by many geologists, the intrusive 

 nature being first recognized by Lawson in 1885. The 

 detailed descriptions of the Haliburton-Bancroft district 

 by Adams and Barlow^ develop two conclusions of im- 

 portance in the present connection. First, the intrusions 

 are in broad domal masses, in which movement went 

 forward during crystallization. Second, the granites 

 profoundly altered the adjacent sediments, and this 

 metamorphism dies out with distance from the intru- 

 sions, the amphibolites and paragneisses of the Grenville 

 passing into blue limestones interbedded with more 

 clastic layers. Where exposed in New England, the 

 Archeozoic is dominantly the Laurentian granite, and the 

 older sediments consist of minor areas profoundly 

 metamorphosed and injected. 



Turning to the Paleozoic intrusions, an inspection of 

 the geologic map of North America will show the large 

 extent to which they outcrop east of the Connecticut 

 River. Between the Connecticut and the Green Mountain 

 axis they occur more sparingly and in smaller areas. 

 This marks the boundary of the batholiths, and farther 

 to the west, in the Taconic synclinorium, even dikes are 

 rare or wanting. Dale has noted an amphibolite intru- 

 sion eight miles west of Pittsfield, Massachusetts. In 

 the region of Franklin Furnace, New Jersey, dikes, 

 mostly basic, volcanic necks filled with breccia, and a 

 laccolithic intrusion of nepheline syenite occur just west 

 of the southward extension of the pre-Cambrian axis. 



The evidence is clear that the New England batholiths 

 reach much wider development at moderate depths below 

 the present surface. Many show domal form to their 

 margins and between them the sediments are in many 

 places so infiltrated with magmatic emanations and cut 

 by pegmatite dikes as to leave no room for doubt that 

 they are the roofs of bodies of granite. The chief struc- 



^ F. D. Adams and A. E. Barlow, Geol. Survey Canada, Mem. 6, 1910. 



