418 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



ever, most of the geological papers relating to Eastern ^Massachusetts 

 T\'ere based on the views of Dr. Hunt as here presented. It may be 

 noticed that the Quincy granite near the Braintree argillite quarry, 

 which Professor Shaler regarded as a quartzite or sandstone, Dr. Hunt 

 calls the same as the Marblehead felsite. 



In Mr. Walling's Atlas of Massachusetts, published in 1871, Prof. C. 

 H. Hitchcock gave a Geological Description of the State (pp. 17-23). 

 He writes : — 



" In New England the older strata have been greatly metamorphosed, i. e., 

 have been transform.ed from the original sedimentary sandstones, clays, and 

 limestones into granite, gneiss, schists, slates, and other crystalline rocks ; and 

 during the process of change the remains of the primeval animals and plants 

 have been mostly obliterated." 



To the Eozoic formation he refers 

 " the syenite and porphyry of Eastern Massachusetts ; and possibly the gneiss 

 and granite of Plymouth and Bristol counties, and the gneiss and hornblende 



schist of Middlesex county Associated with the Paradoxides slates of 



Hingham, is a conglomerate composed of pebbles of syenite and porjihyry, like 

 the ledges of these rocks occupying so much of the area in Essex, Middlesex, 

 Norfolk, and Plymouth counties. The inference is irresistible, that these un- 

 stratified rocks existed as ledges before the birth of the trilobite, occupying the 

 very oldest Paleozoic bed, and therefore they nuist be of Eozoic age. Litho- 

 logically, there is a slight resemblance between some of the porphjTitic rocks 

 and the Huronian group of Canada and Michigan." 



Prof. Hitchcock is in error here, since the age of the Hingham argil- 

 lite is not known, and if it were, the finding of fragments of an eruptive 

 rock in a sedimentary one is no proof of difference in geological age. 



In his Notes on Granitic Rocks Dr. Hunt says : — 



" Felsites and felsite-porphyries are well kno'nm in Eastern Massachusetts at 

 Lynn, Saugus, Marblehead and Newburyport These rocks are through- 

 out this region distinctly stratified, and are closely associated with dioritic, 

 chloritic and epidotic strata. They apparently belong, like these, to the great 

 Huronian system." (Am. Jour. Sci., 1871, (3) I., p. 84.) 



Later, Prof. A. Hyatt remarked : — 



" The porphj-ry of our vicinity, whether Lynn, Marblehead or Newbury- 

 port is a recomposed rock, a conglomerate composed of more or less rounded 

 pebbles of more ancient banded porphyry We meet in the neighbor- 

 hood of Newburyport with a transition rock made up partly of porphyry, and 

 then with stratified diorites and slates, which surround the porphyry outcrop 



on the sea-face The northwesterly dip, and northeasterly strike of these 



diorites and slates, and the presence of slate rocks in Topsfield and Middleton, 



