Hunt.] 



46 [October 19, 



Dr. Hitchcock, described by him as occasionally schistose and pass- 

 ing into hornblende slate, (Geol. Mass., pp. 548, 647) ; and also his 

 varioloid wacke, under which name he describes the green and choc- 

 olate-colored amygdaloidal epidotic and chloritic rocks of Brighton, 

 and the somewhat similar rocks of Saugus, which are seen within a 

 few hundred feet to the northwest of the limit of the red jaspery pe- 

 trosilex. This series of magnesian rocks is apparently identical with 

 that which occurs with dolomite and massive dark colored serpen- 

 tines in the city of Newport, E. I., where the beds have also a high 

 dip to the northwest. A similar series of strata is largely displayed 

 on the islands and along the shores of Passamaquoddy Bay. The 

 dioritic and chloritic beds towards their base are there interstratified 

 with red felsite-porphyries like those of this vicinity, which, asso- 

 ciated with granular eurites, form great masses in that region. I 

 regard these two types of rocks as forming parts of one ancient crys- 

 talline series, which is largely developed in the vicinity of Boston, 

 and may be traced at intervals from Newport to the Bay of Fundy, 

 and beyond. To this same series I refer the great range of gneissic 

 and dioritic rocks with serpentines, chloritic, talcose and epidotic 

 schists which stretches through western New England. 



These ancient rocks are in various places penetrated by intrusive 

 granites, which are generally more or less hornblendic — the syenites 

 of Hitchcock and others. They often contain true feldspars, as in the 

 well-marked granite of Newport, which there cuts the greenish dio- 

 ritic and sometimes amygdaloidal rocks. In this vicinity, besides the 

 granites of Cape Ann and of Quincy, which probably belong to this 

 class, examples of intrusive granites (or syenites) are well seen in 

 Stoneham and in Marblehead, where they cut the greenish chloritic 

 rocks, and on Marblehead Neck, where they are erupted among the 

 felsite-porphyries. In all of these places the phenomena of disrup- 

 tion and enclosure of fragments of the broken rock in the granite are 

 well seen, the lines of contact being always sharp and well-defined. 

 Considerable varieties in the colors and the constitution of these 

 erupted rocks are observed in different localities, and sometimes even 

 in portions of the same mass. This is well seen on Marblehead 

 Neck, where the aspect is such as might result from the simultaneous 

 gushing forth of two somewhat different varieties of granite, as if from 

 contiguous beds of an older granitic gneiss beneath. In one case at 

 Marblehead the eruptive granite is traversed by segregated or endo- 

 genous veins of red orthoclase with quartz and epidote. 



