PRE-CAMBRIAN ROCKS 441 



"1. A central band of phyllite and fine-grained micaceous quartz schist, the 

 Albion schist member, _ 



"2. Two flanking bands of granular massive quartzite, the Grafton quartzite. 



"3. Two broad exterior bands of green schists and amphibolite, the Marlboro 

 formation. 



"4. Thick beds of crystalline limestone, the Smithfield limestone, with inter- 

 calated soapstones and serpentine." 



It has been found that there is no continuous central band of schist as 

 mapped by Emerson and Perry. Instead, there are only occasional out- 

 crops of green schist in a mass of quartzite which is well exposed along 

 the east side of the Blackstone Eiver in rocky ledges. The schist is ap- 

 parently interbedded in the quartzite. The line of the new Grand Trunk 

 Eailway extends along the east side of the river to a point just south of 

 Albion, and the excavations have exposed several contacts of the quartzite 

 and schist. Northwest of Albion, along the New York, New Haven and 

 Hartford Eailroad, there are large outcrops of both quartzite and schist. 

 Interpreting the schist in this manner, it is necessary to adopt the nomen- 

 clature proposed by Woodworth. 



STRUCTURE 



The structure of the Blackstone series is very obscure on account of 

 the large amount of alteration and- metamorphism to which these rocks 

 have been subjected. The series, has in general a northwest-southeast 

 strike and a prevailing dip to the east, usually at a high angle. The cen- 

 tral band of quartzite and interbedded schist is older than the Ashton 

 schists. The evidence of this is, found in the pebbles of quartzite found 

 in the conglomeratic facies of the Ashton schists. The previous workers 

 -in the region have held a similar opinion as to the relative ages of the 

 two formations. The quartzites appear to form a closed anticline, with 

 the Ashton schist on either side. There are several isolated patches of 

 quartzite on the east, indicating that quartzite underlies the Ashton 

 schists in this, locality. It is difficult to account for so broad a band of 

 schist — originally 4 miles or more — on the east, but this is not a valid 

 reason for considering that the series was originally more than two miles 

 in thickness. 



CUMBERLAND QUARTZITE 



The Cumberland quartzite, as here defined, consists of quartzite and 

 interbedded schist. As noted above, the schist can not be distinguished 

 in mapping from the quartzite. The latter is a fine-grained, massive, 

 quite ipure white rock, usually stained light yellow by the introduction of 

 iron oxide. When it is impure, ,thin plates of muscovite have been 

 developed along planes of shearing. By a further increase of mica the 

 rock becomes a schist. 



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