3J8 GEOLOGY OF THE NARRAGANSETT BASEST. 



A mucli thicker bed forms the two exposures at the Lirne Rock light-house, 

 whose strike seems to be approximately east-west, clip steep southward. 

 A bed of limestone more nearly agreeing in thickness with the two occur- 

 rences above described is found on the. promontory a quarter of a mile 

 southwest of Lime Rock. Here again it is prominently associated with the 

 green shale series, and strikes N. 50° to 60° E. and dips steeply northward. 

 Limestone beds are also said to have been struck in penetrating the green 

 shales which underlie Goat Island. These thicker calcite beds, which occur 

 along the southern border of Newport Harbor, are in places coarsely 

 crystalline in consequence of metamorphism, but usually show a fine grain, 

 and, though white within, weather to a peculiar light-brown color. The 

 thinner beds of calcite, however, south of Pirates Cave and in the Little 

 Compton shales are usually tinted with pink or reddish purple. 



So far, in all eastern Massachusetts and Rhode Island, only two forma- 

 tions of Paleozoic age have been discovered, the Cambrian and the Car- 

 boniferous. The Carboniferous is nowhere known to contain true limestone 

 beds of sedimentary origin. 1 The Olenellus Cambrian at almost all of the 

 localities where it is known to occur in these States contains limestone inter- 

 bedded with shales, resembling especially the thinner limestone beds of the 

 green and purple shale series in the southern Narragansett Bay region. In 

 view of these facts search for fossils was made in these southern localities, 

 but without success. The determination of the age of these shales as pre- 

 Carboniferous therefore rests upon two facts — the presence of limestone 

 layers and the entire absence of carbonaceous material in any of these beds. 



If, in addition, the relations of the arkose to the green shale series at 

 Sachuest Neck be taken into account, and the occurrence of the arkoses at 

 the line of contact between the green shale series of supposed pre-Car- 

 boniferous age and the Carboniferous rocks on Conanicut, Rose Island, and 

 Coasters Harbor Island be considered, an assumption of the pre-Carbonif- 

 erous character of the green shale series affords a more ready explanation of 

 the cause of its present distribution, faults having thrown pre-Carboniferous 

 rocks upward on the south side of the faults, against higher-lying Carbonif- 

 erous rocks. 



1 As will be seen from Mr. Woodworth's part of this monograph, there are limestone deposits in 

 the Wauisutta series, but these are probably of secondary origin, owing their formation to the injec- 

 tion of igneous rocks in the area in which they are found. — N. S. S. 



