UPPER CAMBRIAN PEBBLES. 109 



varied of these is in. the northern part of the town of Cumberland, where, 

 in the area about Sneech Pond, ores of copper and iron occur, replacing 

 portions of the limestone, angular brecciated fragments of which lie in 

 the ore-bearing mass. The iron of the old mine in Cranston, in the "dug- 

 way," is probably a ferruginous replacement of the limestone. The Sneech 

 Pond ore bodies above mentioned are near eruptive rocks, but whether the 

 deposits have originated through the action of heated waters or through the 

 downward percolation of acidulated surface waters, the field itself does not, 

 in the present condition of the openings, give opportunity for determining. 



CAMBRIAN PERIOD. 

 LOWER CAMBRIAN. 



Rocks comprised within the limits of the formations now denominated 

 Cambrian were referred to vaguely as early as 1844 by Ebenezer Emmons, 

 but the discovery of demonstrable Cambrian strata in this field was not 

 announced until 1888, when Professor Shaler and Dr. A. F. Foerste pub- 

 lished the account of the fossils found by them in North Attleboro, Massa- 

 chusetts. For a further notice of these rocks the reader is referred to Dr. 

 Foerste's description in Part III of this monograph. 



MIDDLE CAMBRIAN. 



Beds of Middle Cambrian age have not been discovered south of the 

 area about Weymouth and Braintree, where they are known to occur. 



UPPER CAMBRIAN. 



(Not known in place.) 



Postdam. W. B. Rogers: Proc. Boston Soc. Nat. Hist., Vol. VII, 1861, pp. 389-391. 

 Primordial. Crosby and Barton: Am. Jour. Sci., 3d series, Vol. XX, 1880, pp. 416-420. 

 Upper Cambrian. C. D. Walcott: Am. Jour. Sci., 4th series, Vol. VI, 1898, pp. 327-328. 



In 1861 it was pointed out that the coarse conglomerates of the southern 

 portion of the Carboniferous field contained quartzite pebbles carrying two 

 species of Lingula (L. prima and L. antiqua) referable to the Potsdam sand- 

 stone. In 1880 Crosby and Barton announced the occurrence of Scolithus 

 linearis in the same conglomerate pebbles near Newport, Rhode Island. 



During the present survey the writer has found these fossiliferous 

 pebbles farther north and east than the localities described by earlier 

 investigators. Other occurrences are noted in Dr. Foerste's section of this 



