EASTERN MASSACHUSETTS. 



41 



o 



the rock lias assumed something of tlic nppeanuicc of guei^^s, and would by 



some be classed in tluit group of rocks The uiiiroiiu dip away I'rom the 



Quiiicy Hills, shown by all I he stratified beds on their (lauks, may he regarded 

 as sullicient proof that their elevation came after the deposiuou of these beds." 

 (Proc. Best. Soc. Nat. Hist., 18()9-7l, XIIL, pp. 172-178.) 



While to one not acquainted with the geological structure of the re- 

 gion described, Professor Shaler's paper may appear couclnsive; the 

 facts, that the granite presents exactly the same intrusive relations to 

 the argiilitc that he says it should have if eruptive ] that he mistook for 

 sandstones and quartzites tlic Q.iiiucy granite itself; that the fossils in 

 the argillite show that its dip is diametrically the opposite of the one ho 

 has assumed ; that his supposed I'ipplo-marka were tlie not uncommon 

 wavy fracture of granite ; and finally that his assumed stratilication 



plan.es are joint or structure pLmes, — leave his conclusions without any 

 foundation.* 



, Professor Shaler points to the relations between the argillite and con- 

 glomerate as exposed while the excavations were being made for the 

 conalnictiou of the Chestnut Hill P.eservoir. There he found that the 

 argillites lay beneath with conglomerate overlying, then more argillite 

 and above this the conglomerate, indicating it as pi'obable that tJie argil- 

 lites and conglomerates in the vicinity of Boston form the same series of 

 beds, which ho considered to belong to the primordial era. (/. c, p. 17G.) 

 In 1870, Dr. Hunt, on account of the finding of Eozoou Canadetise in 

 limestones at Newbury (erronocmsly said to be in the adjoining town, 

 Newbm-yport) and Chelmsford, regarded the associated rocks as being of 



Lauren liau ago, saying : — 



" These specimens from Clielmsford, it shouLl be said, liave been examined 

 and satisfactorily identi lied by Dr. Dawson. The arguLueiit from miueralogi- 

 cal and lithological resemblauecs in favor of the Laurentian age of the lime- 

 stone in question is therefore now supported by the undoubted presence in 

 them of Eozoon Canadense.^' 



The rocks about Newbury, which it will be recollected were muted 

 by Prof. C. IT. Hitchcock to the Capo Ann and Quincy hornblcnilic 



* In the preceding paper of Professor Slialur the misnoinor of " Cand)ridge slates " 

 was applied to tliu argillites so well exposed in Soincrvillc, and whicli properly slionUl 

 have been eaUed by llic name of that city instead of Ctiuihridge. The truth is, that 

 the locality from wliich tlu'y were named was erroneously su]iposcd to lie in Ona- 

 hiidge, when in fact it is in Sotnervillo. This localitv wasaffiin orronconslv said to 

 bo in Cambridge in Professor Sluder's " Qnestion Guide to the Environs of Button," 

 1875, p. 20. No exposure of the argillite ia known to exist in Cambridge, although 

 it has been foruid there by digging. 



