" Simple Petrosilex 



EASTERN MASSACHUSETTS. 399 



The felsparoid was divided as follows : Common, Quartzose, Epido- 

 tic, and Granitic Felsparoid. 



The felsite he classes under the head of Petrosilex, but thinks that, 

 instead of petrosilex being a simple mineral, as it was then generally- 

 regarded, possibly it might be compound in its nature. 



He makes the following divisions of the petrosilex : — 



' Flinty Petrosilex. 

 Sonorous " 

 Jasper " 



. Novacular " 

 " Porphyritic Petrosilex." 



The name simj^le petrosilex seems to have been confined to the more 

 apparently homogeneous fclsites, while the term j)orphyritic petrosilex 

 was given to those rocks supposed to have a base of simple petrosilex, 

 or of felsparoid which held enclosed porphyritic crystals. The simple 

 petrosilex was thought to pass into wacke and felsparoid. 



The common argillite of the country was denominated argilloicl, and 

 it was supposed to pass into petrosilex. He separated it into the fol- 

 lowing divisions : Common and Novacular Argilloid. An imperfect 

 chemical analysis was made of some of the argilloid that resembled the 

 sonorous petrosilex. 



The conglomerate of the district was called wacke. Mr. Godon says 

 of it : — 



" How much attention soever I have paid to the examination of this rock in 

 situ, I have never observed in it any distinct stratification. It commonly 

 unites with the rocks previously described, and with amygdaloid, often by an 

 insensible transition. I possess specimens, which, on pieces of four inches 

 square each, present its different passages to felsparoid, amphiboloid, simple 

 and porphyritic petrosilex, argilloid, «&c." 



His explanation of its origin is interesting, not only as illustrating 

 some of the views of that time, but also from its general resemblance to 

 the conclusions and statements in some more recent articles on the geol- 

 ogy of Eastern Massachusetts. 



" If permitted to venture an opinion on the mode of its formation, we may 

 suppose,'that, as we find in it specimens of almost all the rocks, which pre- 

 dominate in the country, it originated from a motion, which disturbed and 

 divided the vast deposits of felspathic, porphyritic, petrosiliceous, &c. rocks, 

 while they were passing from the state of fluidity to that of solidity. This 

 motion ought to be supposed as having taken place before the complete solidi- 

 fication of these rocks ; since the compactness of the wacke indicates that its 



