39 



inextricable confusion as to force the conclusion, that at least 

 one of these rocks has been fluent ; and near the lake shore, 

 enclosed in the granite, are angular fragments of a schist 

 resembling that on Marblehead Neck. The same phenomenon 

 has been observed by Prof. Hyatt and myself at many points 

 in Peabody and Lynnfield, especially in the quarries about the 

 village of Peabody, and along the western border of this large 

 granitic area. In North Saugus, on the high hills to the west 

 of the private road running north from Forest Street and 

 Central Brook to Water Street we have, perhaps, the finest 

 example of the extravasation of the granite yet observed 

 in this region. The exposures of the rock here are re- 

 markably good ; and the granite is coarse and sharply defined, 

 where it penetrates the adjoining petrosilex and hornblende 

 slate in irregular dykes, or envelops isolated masses of 

 these rocks that have been wrested from the parent beds. 

 The relation of the granite and stratified rocks along the rail- 

 road in Natick appears to approximate to this in part. In 

 the western part of Wrentham, about one-half mile from 

 the western boundary of the town, and the same distance north 

 of the Rhode Island line, what appears to be Huronian granite 

 has been observed cutting fine-grained schists that I refer to 

 the Montalban age. To the north of this, about Wads- 

 worth's Station on the New York and New England Kailroad, 

 and generally throughout this southern region, especially in 

 Foxborough, Sharon, Canton, Franklin, etc., the granite and 

 diorite are so related that one must be exotic, probably both. 



A glance at the map sufiices to show that the geographical 

 distribution of the granite is in harmony with the theory of its 

 extravasation ; for it is seen to occur among the other members 

 of the Huronian series in a manner decidedly irregular. It 

 does not form continuous, well-defined areas ; but is found in 

 isolated patches, with boundaries difficult to define, and such 

 as can be readily accounted for only on the supposition of a 

 former plastic or fluent condition of this rock. The large area 

 marked as granite between Boston Harbor and the Carbonif- 



