418 



THE AZOIC SYSTEM AND ITS SUCDIYISIONS. 



ever, most of the geological papers relating to Eastern ^[assaehusetts 

 ■wore based on the views of Dr. Hunt as here presented. It niay bo 

 noticed that the Quincy granite near the Braintree argillitc quarry, 

 wliich Professor Shaler regarded as a quartzitc or sandstone. Dr. hfunt 

 calls the same as the Marblehoad felsite. 



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

 PI. Hitchcock gave a Geological Description of the State ([)p. 17-23). 

 Pie writes ; -— 



'•'• In New England the older strata have been greatly mdainorplioscd ^ i. c, 

 have been transrornicil from the original sediiuentary saudslotu^s, clays, and 

 limestones into gra]iito, gneiss, scliists, slates^ and other caystalliiu; rocks ; and 

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

 have Ijeen mostly obliterateih" 



To the Eozoic fornration he refers 



" tlie syenite and ]jor[)]]yry of Eastern ]\rassachnsetts ; and possibly the gneiss 

 and CTanite of Plvmoutli aud Bristol countic^s, and the 'nieiss and lioriibleinle 



schist of Middlesex county Associated "with the Paradoxides slates of 



ITiugliam, is a couglonuirate composed of pebbles of syenite and porphyry, like 

 the leilL^es of these rocks occupying so jiuicli ot the urea in Essex, ]\iiildlesex, 

 Noi'folk, and Plyjuouth counties. The inference is irresistilde, that these uji- 

 stral:ilied rocks existiid as ledges before the birth of llie trilobite, occupying the 

 very oldest Paleozoic ])eil, and therefore they nnist be of Eozoic age. Litho- 

 logically, there is a slight resemblance Ixjtween some of the po]'ph3-ritic r'.)cks 

 ajid the Iluronian group of Canada and Michigan." 



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

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

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



In his Notes on Granitic Bocks Dr. Hunt says : 



" Felsites and felsite-porphyries are well known hi Eastern Massachusetts at 

 Lynn, Saugus, Marblehead and Newl.)uryport These rocks are through- 

 out this region distinctly stratified, and are cloHcly associated wJlIi diorilic., 

 cbloritic and epidotic strata. TInsy apparently belong, like these, to the great 

 Iluronian systcnn" (Am. Jour. Sci., 1871, (3) T., p. 81.) 



Later, Prof. A. Hyatt remarked : — ■ 



"The porphyry of our vicim'ly, whether Lynn, Marblehead or Newbury- 

 port is a recomposed rock, a conglomerate composed of more or less n.auided 



pebl)l(.'s of more ancient l.)anded porphyry We meet in the neighbor- 



liood of Kewburyport with a transition rock made np ))arlly of porph}'ry, and 

 tlien with stratified diorites and slales. which surround the porpliyry outcrop 



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



diorites and slates, and the presence of slate rocks in TopsHeld and MkUlleton, 



