460 WARREX AND POWERS DIAMOND HILL-CUMBERLAND DISTRICT 



buff-colored sandstone or quartzite within 50 feet of the granite. This 

 outcrop is now exposed onW when the water in the adjoining reservoir 

 is exceptionally low, but unfortunately the actual contact is even then 

 under the groundwater level and can not, therefore, be seen. The granite 

 is considered to be intrusive for the following reasons: (1) The strike 

 of the Lower Cambrian fossiliferous sediments is in part at high angles 

 to the line of outcrop of the granite; (2) the dip of the Cambrian is ai 

 a high angle, usually toward the granite; (3) the line of outcrop of the 

 granite is irregular, apparently due to intrusion and not to faulting; 

 (4) the Cambrian sediments nearest the granite are, in outcrops within 

 a few hundred feet of each other, red shale, limestone, and sandstone — 

 a relation which could not be brought about by simple faulting.^*^ 



Many years ago excavations were made on the west side of Hoppin Hill 

 which showed the granite in fault contact with the sediments. The gran- 

 ite has been considered to be pre-Cambrian because it was coarsely crys- 

 talline in its nearest outcrops to the Cambrian and because the latter 

 showed no evidences of contact metamorphism. This reasoning does not 

 seem sufficient to the writers to place the granite in the pre-Cambrian, 

 for experience in this field generally shows that such granites sometimes 

 remain coarse grained to within a few inches of their contact, nor do the 

 sediments necessarily show evidences of strong metamorphism at distances 

 as great as 50 feet from the contacts. 



The only other evidence concerning the age of the granites is unsatis- 

 factory. As discussed above, Foerste found Cambrian boulders on the 

 Joes Eock granite hill south of West ^\'rentham. Furthermore, he says: 



"Along the brow of the hill westward, the granite is seen to inclose long 

 thin layers of an argillitic purplish or brownish rock, which may possibly be 

 fragments of the Olenellus Cambrian shale hardened by metamorphism. It is 

 impossible to determine from these inclusions whether the granite of these 

 regions is to be considered as pre- or post-Cambrian in age. If the fragmental 

 inclusions referred to be Olenellus Cambrian shales the granite must evidently 

 be considered as post-Cambrian." 



These inclusions of metamorphosed slate are, in our opinion, Lower 

 Cambrian. From tliis and the other evidence presented in the field it 

 seems best to date the subalkaline granites as post-Lower Cambrian. The 

 age of the earlier series of Paleozoic biotite granites of New England 

 must, we believe, be determined from relations found in Maine and in 

 Xova Scotia. Xear Eastport, Maine, the granites cut Silurian volcanics 

 and pebbles of the granites are found in the Perry Basin sediments of 

 Chemung (Upper Devonian) age. At Torbrook, Nictaux, Xova Scotia, 



» For a map of a part of this localitj- see U. S. Geol. Survey Monograph 33. plate 31 



