388 GEOLOGY OF THE NAKRAGANSETT BASIN. 



arriving at a correct knowledge of the lithological characteristics of the 

 Olenellus Cambrian in eastern Massachusetts. Instead of being a forma- 

 tion in which sandstones and conglomerates form a predominating element, 

 the Olenellus Cambrian of eastern Massachusetts, as at present recognized, 

 consists chiefly of reddish and greenish shales and slates with whitish and 

 reddish layers and nodules of limestone. Sandstone beds are known at 

 almost all exposures, but form only a very unimportant element of the 

 Olenellus Cambrian, as far as this horizon has been definitely recognized. 



Some sandstone is, for instance, found associated with the reddish 

 shales and limestone beds discovered in 1889 by the writer at locality 4, 

 just north of the State line, a short distance east of the road leading from 

 West Wrentham to Diamond Hill. 



North of Mill Cove, in the Boston Basin, the Olenellus Cambrian 

 (fossils discovered by the writer in May, 1889) consists chiefly of reddish 

 and cherty greenish slate, including limestone nodules, and a few limestone 

 beds, the latter containing Hyolithes communis and HyoUthellus micans. 



At the southern end of Nahant the Olenellus Cambrian (fossils first 

 recognized by the writer 1 in April, 1889, but previously discovered and not 

 identified by Prof. Alfred C. Lane and J. Sears) consists of cherty greenish 

 slate, with two or three white limestone layers, the latter containing Hyolithes 

 communis and a small form of Stenotheca rugosa. Near the southwestern 

 angle of Topsfield similar cherty greenish slates occur, the fossiliferous 

 limestone being, however, hard and light blue in color. 



At Achelaus Hill, in West Newbury, Mr. John Sears reports another 

 instance of cherty slates similar to those at Nahant, and containing similar 

 fossils. 



No great masses of sandstone and conglomerate have so far been 

 recognized as belonging to the Olenellus Cambrian horizon, or as being 

 closely associated with the same. 



CAMBRIAN BROOK LOCALITIES. 



LOCALITIES 1 AND 2, SOUTHWEST OF NORTH ATTLEBORO. 



A great mass of quartzite on the southeastern side of Hoppiu Hill 

 may belong to the Olenellus Cambrian. Fragments of reddish shale occur 

 in the soil farther eastward. 



1 See The paleontological horizon of the limestone at Nahant, Massachusetts: Proc. Boston Soc. 

 Nat. Hist., Vol. XXIV, 1889. 



