Bouv(§.] 218 [January 19, 



changed by lieat and other agencies from its original character to 

 such as it now presents. In referring to Hitchcock's work I will 

 say that there are now no more instructive views presented upon 

 the porphyries and sienites of Massachusetts than can be found in 

 its pages, notwithstanding the lapse of a third of a century since it 

 was written, and the attention that has been given to these classes of 

 rocks by eminent geologists. 



I may be pardoned now if I refer to my own conclusions of many 

 years past. I had been in the habit of examining as closely as pos- 

 sible the specimens of the red compact feldspar, the Felsite of Hing- 

 ham, and though this presented itself to me of quite homogeneous 

 structure, I came to regard it as derived from a source, the announce- 

 ment of which seemed to me at the time too absurd to make. At a 

 meeting however, of the Boston Society of Natural History, on April 

 2, 18G2, I ventured to ask Dr. Jackson if he had observed evidence of 

 metamorphic action in the conglomerate rocks of our neighborhood, 

 stating that I had noticed by the waysides of Hingham, a blood red 

 rock resembling red jasper, which I had suspected to be altered con- 

 glomerate, though I had not until then discovered anything of a 

 pebbly or slaty characte in it, but had just found a locality where 

 its derivation from the conglomerate could be traced. 



This view of the origin of our felsite rocks was not, I think, 

 regarded with much favor, and the subject was not apparently con- 

 sidered by observers until some years after. In 1870 Dr. Hunt pre- 

 sented a p'aper before the Boston Society of Natural History, in 

 which he considered the rocks found in the vicinity of Boston, as 

 embraced in three classes, viz : — 



1. Crystalline stratified rocks. 



2. Eruptive granites. 



3. Unaltered slates, sandstones and conglomerates. 



The first class, the crystalline stratified rocks, he again subdivided 

 lithologically, making one division to consist of the felsite porphy- 

 ries with the associated non-porphyritic jasper-like varieties, and 

 the other of the epidotic, chloritic rocks, including the serpentines 

 and amygdaloids. These two divisions he regarded as forming parts 

 of one great, ancient, crystalline series of rocks which could be 

 traced from Newport to the Bay of Fundy. In the discussion that 

 followed the reading of Dr. Hunt's paper, Professor Niles distinctly 

 stated that he had traced in Dedham the conglomerate until it passed 

 into porphyry. He had noticed the effects of metamorphism where 



