416 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



reritian ago. 



') 



granites (syenites), Dr. Hunt regards as unlike tlio latter. (Am. Jour. 

 Sci., 1870, (2) XLIX., pp. 75-78.) 



In a paper published in 1870, but said to have been read before the 

 American Association in August, 1800, Dr. Hunt remarks : "The gneiss 

 of Eastern Massachusetts is, as I have recently found, in part of Lau- 



(Am. Jour. Sci., 1870, (2) XLIX, j). 184.) Again, the 

 same year, the " diorites and porphyries" at Newburyport, Salem, 

 Lynn, and Marblehead were referred to the Cambrian, which Dr. Hunt 

 at that time appears to have regarded as the equivalent of the Huro- 

 nian. (Am. Jour. Sci., 1870, (2) L., p. 89.) Further, of his Terranovan 

 series he states : ~ 



" The micaceous and hornblendic schists, with interstratified fine gramed 

 whitish gneisses (locally known as granites) which I have seen in HallowcU, 

 Augusta, Brunswick and Westbrook, in Maine, appear to belong to the same 

 series ; which will also probably include nmch of the gneiss and mica-schist of 

 Eastern New England. If this upper series is to be identified with the crystal- 

 line schists which, in Hastings County, Ontario, overlie, unconforniably, the 

 Laureniian, and yet contain Eowon CanadensGj the presence of this fossil can no 

 longer serve to identify the Laurentian system. To this lower horizon how- 

 ever, I have referred a belt of gneissic rocks in Eastern Massachusetts, which 

 are lithologically unlike the present series, and identical with the Laurentian 

 of New York and Canada." (/. c, p. 88.) 



In October, 1870, Dr. Hunt stated regarding the geology of Eastern 



Massachusetts, that 



" the rocks which we have seen may be considered in three classes. A, the 

 crystalline stratified rocks ; B, the eruptive granites ; C, the unaltered slates, 

 sandstones and conglomerates. The former of these may be separated litho- 

 logically into two divisions ; the first being the quartzo-feldspathic rocks. 

 Among these are included the felsite-porphyrites of Lynn, Saugus and Marble- 

 head, with their associated non-porphyritic and jasper-like varieties 



Associated with them is a granular quartzo-feldspathic rock, which is often 

 itself porphyritic, with feldspar crystals, and sometimes appears as a fine 



grained syenitic or gneissoid rock, often distinctly stratified These 



rocks are seen intimately associated with the porphyry on Marblehead Neck, 

 also in Marblehead, and underlying the argillites of Braintree and Weymouth. 

 The second division of the rocks of class A includes a series of dioritic and 

 chloritic rocks, generally greenish in color, sometimes schistose, and frequently 



amygdaloidal This series holds a bed of dolomite at Stoneham, and 



serpentine in Lynnfield, .... the greenstones of Dr. Hitchcock . . . . ; and 

 also his varioloid wacke, under which name he describes the green and choco- 

 late-colored amygdaloidal epidotic and chloritic rocks of Brighton, and the 

 somewhat similar rocks of Saugus I regard these two types of rocks as 



