62 GEOLOGY OF THE NAKBAGANSETT BASIN. 



RED COIjOR OF THE CAMBRIAN AND THE CARBONIFEROUS. 



The red hue of certain portions of the Cambrian as well as of the 

 Carboniferous rocks affords a matter for inquiry. Though no solution of 

 the problem has been attained, it may be well to note certain facts of possi- 

 ble value to those who may hereafter attack the question. It is noteworthy 

 that the red beds of both the above-mentioned series occur on the western 

 and northern sides of the Narragansett Basin and in the trough of the 

 Norfolk Basin. In both these sections the red beds are somewhat irregu- 

 larly distributed, generally occurring between deposits which have no trace 

 of the peculiar hue. In some cases, as noted by Mr. Woodworth, the red 

 stratum may be but a few inches thick, lying between sandstones or arkoses 

 of a whitish hue. This peculiarity of distribution is also very noticeable 

 in deposits exhibited at Gay Head and elsewhere on Marthas Vineyard 

 which, in Cretaceous and Tertiary time, were made under conditions some- 

 what similar to those which existed in the earlier periods when the Narra- 

 gansett deposits were formed. 



It seems likely that the red hue of stratified deposits is due to a variety 

 of actions. In some instances, as along the present coast line of the reg-ion 

 and about the mouth of the St. Lawrence, red beds may be formed by the 

 disintegration of Triassic or other red sandstones and clays, the rearranged 

 material retaining in large measure the hue of the rocks whence the debris 

 came. In other instances, perhajDS in the case of the Cambrian and possi- 

 bly the Carboniferous of the Narragansett field, the red hue may be due to 

 the fact that the beds thus colored originally contained a share of lime car- 

 bonate. Downward-percolating waters containing iron oxide transformed 

 these beds first into impure siderite, and further change served to bring the 

 iron into the state of limonite. The coloration thus brought about is fre- 

 quently to be observed in the Devonian and Silurian rocks of the Appala- 

 chian district, being particularly conspicuous in the iron-bearing members 

 of the lower Devonian and upper Silurian strata of eastern Kentucky, as 

 for instance in Bath County. In yet other instances the decay of crystal- 

 line rocks containing a considerable share of iron may have provided the 

 ferruginous material in a direct manner in the process of sedimentation. 

 Some unpublished studies as to the amount of magnetic oxide in the drift 

 covering which exists in this part of New England have shown me that the 



