EASTERN MASSACHUSETTS. 



419 



are clifTicult to account for unless we imagine tlie porphyries to be iuterstrati- 

 fied with them, llie succession of the strata in this part of the country then 

 would be Eozoonal limestones and serpentines, then slates, then the porphyries 

 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 iu the porphyry. In cither case all the porphyries are 

 probal)ly older tlian tlie Eozooiiul rocks of Newburyport, and underlie 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 

 Lave been several which overspread the surface of the country." (Bull. Essex 

 Inst., 187 L, IIL, pp. 49-53.) 



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



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ows : 



" 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, chlorilic and epidotic rocks), to the Iluronian 

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

 from eastern Massachusetts, wliich 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 wdiich I consider newer than the 

 Huronian, and the ecpuvalent of thcAVhite Mountain gneisses and nnca-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 limest(nies 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 por])hyry, on 

 which it often rei)ose8, and from the ruins of which it is derived." (Bull. 

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



If the reader will refer to our quotation of Dr. Hnnt*s paper relating 

 to tlie Eozoiin, 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 hi/poiheticalj and not a positive one, as Dr. Hunt now claims it to have 

 been. In connection with the above qiu)tatlon from the Pulletin of the 

 Essex Institute it may be interestinii; to remember tluit a little over a 



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