272 THE CAMBRIAN. [bull. 81. 



for determining the geologic age of the deposit. On the east the Coal 

 Measures of the Narragansett Basin occur. On the west side he con- 

 siders the rocks to be of pre-Cainbrian age. as they consist mainly of 

 gneissoid rocks of various composition, and a great area of dark green- 

 ish chloritic deposits which appear in part at least to be metamor- 

 phosed conglomorates and shales. Owing to the large amount of drift 

 material covering the country, no absolute contact with the pre-Cam- 

 brian rocks was observed, nor is the overlap of the Carboniferous upon 

 the Cambrian shown in any section. 

 Of the rocks he says : 



The Cambrian rocks exhibit very little sign of raetamorphic action. The shales 

 indicate a slight amount of infiltration, and in the conglomerates the pebbles all re- 

 tain essentially their original character, save that they are sometimes slightly in- 

 dented one into the other. The cement of the mass is not more altered than is usual 

 with our unchanged conglomerates. Its general characters, save for its reddish color, 

 is undistinguishable from the deposits of Millstone grit age in the neighboring coal 

 fields. 1 



So far fossils have been found in rocks of this section which probably do not in 

 the aggregate include more than 100 feet or so of the total section of the Cambrian 

 series. However, as these deposits are of the same aspect, as all the red slates 

 and conglomerates of the area, it appears at present reasonable to include all 

 rocks of this description with the above-mentioned series. The total thickness of 

 the section which I have termed Cambrian is not accurately determinable. It proba- 

 tly amounts to not far from 2,000 feet. In the main it consists of thin bedded shaly 

 layers which occasionally pass into moderately thick, fine grained, greenish and red- 

 dish slates. Intermingled with these in several levels we have a number of layers 

 of conglomerate, perhaps as many as half a dozen distinct beds, varying in thickness 

 from 200 to 300 feet. In all cases these conglomerates are frequently interrupted by 

 thin layers of shale or sandstone. * * * The rocks from which the pebbles were 

 taken are mainly identifiable in the western portion of the field before described. 3 



The sediments composing this Cambrian section appear to have been derived from 

 rocks substantially' the same as those which now lie in the field west of the area. 

 Although fossils have been found in a small part of the section, close study makes it 

 plain that by far the greater portion of the strata are clearly azoic. The frequent 

 return of conglomerate layers and the coarseness of the pebbles show that during 

 most of the time when the beds were accumulating the region was near shore; so, 

 too, the large amount of sandy matter oven in the slates affords a presumption that 

 the region was not remote from the coast line. About 100 feet of shale beds have 

 been subjected to a very careful search for organic remains. The total thickuess of 

 the deposits in which any trace of life has been found probably does not exceed 100 

 feet, and even in this section only a small part of the rocks actually contain fossils. 3 



Prof. Shaler suggests that the conglomerates were accumulated dur- 

 ing an ice epoch ; and he presents several arguments for this view. He 

 states that the relations of the beds carrying the fauna at North Attle- 

 borough with those of the Paradoxides zone of Braintree are not dis- 

 coverable by comparison with the Massachusetts Bay and Narragansett 

 deposits. At the time he wrote the stratigraphic relation of the Ole- 

 nellus fauna as found at North Attleborough with the Paradoxides 

 fauna was not known, except that the Scandinavian geologists state 



1 Op. cit., pp. 18, 17. »Op. cit., p. 18. *Op. cit., p. 20. 



