434 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



that the Huroniaii granites of this region are mainly exotic. We have seldom 

 far to look to find, in the form of enclosed, angular fragments of clearly-strati- 

 fied rocks, evidence of their extravasation ; and near the Lomidaries of the 

 granites we often observe them cutting the adjoining rocks, especially if these 

 are stratified, in a manner incompatible with any theory that would regard 



them, in their present condition, as chiefly indigenous Believing with 



Prof. Shaler, and also with Mr. T. T. Bouvd, that all these granites are meta- 

 morphosed sediments, I conceive that the peculiar planes of separation (joint 

 structure) referred to by Prof. Shaler demaiid a different interjiretation from 

 that proposed by him, for evidence is not wanting of the extravasation of the 

 granite at many points along the Blue Hill or Quincy and Milton range. 

 .... It is well known that the Quincy granite is met along its northern bor- 

 der by conglomerate and slate The actual contact of this rock with the 



granite is displayed, however, at a place about 5 mile west of the Old Col- 

 ony E. E The contact line is extremely irregular ; and the relation 



of the granite to the semi-crystalline rock is unquestionably that of an exotic. 

 Some three miles to the southwest, it is yery distinctly cut by dykes and irreg- 

 ular strings of the underlying and surrounding granite. According to Prof. 

 W. H. Niles, the relations of the granite and slate on Weymouth Fore Eiver, 

 near the trilobite quarry, affords equally conclusive evidence that at least a 

 portion of the granite has experienced some extravasation since the deposition 

 of the slate. The slates on the South Shore E. E., immediately east of the 

 station at Weymouth Landing, are in contact with the granite, which cuts 

 through, and overlies them in a manner possible, apparently only with an. 

 exotic ; and at the contact of the granite and slate, southwest of the station, 

 Prof. Niles has observed angular fragments of slate actually enclosed in the 

 granite, though lying only a few inches from their original positions in the 

 parent bed. The induration, as if by heat, of the slate and conglomerate at 

 most points where they adjoin the granite, and the frequent development of 

 amygdaloidal characters in the slate in those places, are also facts which tell 

 strongly in favor of the former igneous condition of the granite. The evi- 

 dence of the extravasation of the granite afforded by a study of its relations to 

 the uncrystalline rocks appears to be sufficiently conclusive as regards the por- 

 tions of granite immediately involved At Hospital Point on the Bev- 

 erly shore, near the water's edge south of the lighthouse, is a considerable mass 

 of distinct mica-slate enclosed in the coarse, structureless granite. A smaller 

 mass of a similar stratified schist is enclosed in the granite near the northern 

 end of the railroad-cut in Beverly. On Marblehead Neck the relations of the 

 granite to the fine-grained, distinctly stratified schist occurring there, are such 

 as to leave no doubt that the granite is exotic. Along the shore, at the south- 

 western end of the neck, the exposures are magnificent, and one can see, espe- 

 cially at low tide, numerous angular, ragged, contorted masses of the schist, of 



various sizes, enveloped by the granite It has been set down by all 



observers as the oldest rock in this region, and this view is abundantly justi- 

 fied (except as regards the Naugus Head series), not only by its generally 



