EASTERN MASSACHUSETTS. 419 



are difficult to account for unless we imagine the porphjTies to be interstrati- 

 fieil with them. The succession of the strata in this part of the country then 

 woukl be Eozoonal limestones and serpentines, then slates, then the poqjhyries 

 of Kent's Island and Lynn, then slates and, diorites, and lastly, the porphyries 

 of Marblehead Neck. Either this is the explanation or else we have several 

 anticlinal axes or folds in the })orphyry. In either case all the por[)li\Ties are 

 probably older than the Eozoonal rocks of Newburyport, and undi-rlie them. 

 The porphyry of Marblehead Neck has the stratified micaceous rocks .... 

 lying upon its southeastern face, with dip and strike precisely conformable to 

 the more ancient shore-line formed by the porphyry itself. The porphyry of 

 Lynn has upon its eastern face the outcropping edges of an enormous overflow 



of igneous granite In fact, all the difficulties of the survey have arisen 



from the enormous sheet, or rather, sheets of igneous rocks, for there seems to 

 have been several which overspread the siirface of the country." (Bull. Essex 

 Inst., 1871, III., pp. 49-53.) 



Dr. Hunt, in reply to Prof. Hyatt's communication, remarked as fol- 

 lows : — 



" I have expressed the opinion that the porphyries of the eastern coast of 

 Massachusetts are stratified rocks, belonging, together with their associated 

 diorites and slates (greenstones, chloritic and epidotic rocks), to the Huronian 

 system, or Green Mountain system. As regards the limestones with Eozoon, 

 from eastern Massachusetts, which in the American Journal for Jan., 1870, 

 I referred to the more ancient Laurentian system. I have in that same journal 

 for July, 1870, pointed out the fact that the Eozoon of Hastings county, On- 

 tario, occurs in a series of crystalline schists which I consider newer than the 

 Huronian, and the equivalent of the White Mountain gneisses and mica-schists, 

 so that, as I there remark ' the presence of this fossil can no longer serve to 

 identify the Laurentian system.' .... It will therefore remain for farther 

 study, to determine how far the crystalline limestones of eastern Massachusetts 

 belong to the Laurentian, and whether some of them are not included in one 

 or the other of the newer systems of crystalline schists. The porphyry con- 

 glomerate noticed by the late President Hitchcock and described by Prof. 

 Hyatt, are referred to in my paper of last October, mentioned above. This 

 rock is, I conceive, to be distinguished from the old Huronian porphyry, on 

 which it often reposes, and from tlie ruins of which it is derived." (BuU. 

 Essex Inst., 1871, III., pp. 53, 54.) 



If the reader will refer to our quotation of Dr. Hunt's paper relating 

 to the Eozoon, or to the original (Am. Jour. Sci., 1870, (2) L., p. 88), he 

 will see that the remark regarding the value of that supposed fossil was 

 a hypothetical, and not a positive one, as Dr. Hunt now claims it to have 

 been. In connection with the above quotation from the Bulletin of the 

 Essex Institute it may be interesting to remember that a little over a 



