366 L. V. Pirsson — Geology of Conanicut Island. 



Historical. — We are indebted, so far as I have been able to 

 discover, to Jackson* for the first map and geological descrip- 

 tion of Conanicut. He regards the shales forming the main 

 portion of the island as of Carboniferous age and the granite 

 as intrusive in nature and describes very clearly and correctly 

 the metamorphoses suffered by sedimentaries by the intrusion 

 of an igneous rock. He also gives a few dips and strikes that 

 are in the main correct. The same views were also held by 

 President Hitchcock. f It is to be noted that these observers 

 correlated the granite and other rocks with the granite and 

 rocks on Newport Neck adjacent. They were substantially 

 the views of C. H. Hitchcock;}; and also of T. Sterry Hunt§ 

 except slight variations as to the age of a portion of the sedi- 

 mentary beds at Newport. Various papers have been pub- 

 lished by different authors also on the Narragansett basin as a 

 whole, treating the subject from various points of view. Since, 

 however, in so far as Conanicut is concerned, they do not 

 appear to be based on personal observation and the island is 

 not directly named, they are not given here. For a list of 

 them the reader is referred to a paper by T. N. Dale.f This 

 latter author in 1884T gives in a paper on the geology of the 

 lower part of the basin, a pretty full account of Conanicut, 

 based chiefly on a series of stratigraphical studies. He correlates 

 the granite with that on Newport Neck and on stratigraphical 

 grounds does not regard it as intrusive but as the lowest of his 

 series and a metamorphic product. He describes the lithologic 

 character of the various schists, shales, etc., and gives a large 

 number of dips and strikes. Since, however, Dale, on Conani- 

 cut at least, mistook slaty cleavage for bedding, his conclu- 

 sions, based as they are on largely mistaken stratigraphy, can- 

 not be admitted. That this mistake was made, is evident, not 

 alone from the given dips and strikes, bnt in the paper itself, 

 where he several times mentions the shales as being u striped 

 across the bedding." This striping is however the original bed- 

 ding cut across by slaty cleavage ; in many places on Conanicut 

 the cleavage and bedding are parallel but generally not. 



Geologically the sedimentary beds of Conanicut are of Car- 

 boniferous age, as is shown by their correlation with the coal- 

 bearing strata of the region. Moreover on the most western 

 point of the main portion at X, tig. 1, fossil plants are found of 

 Carboniferous species according to Dr. A. E. Foerste. In 

 general these sedimentaries are made up of an extremely 

 fissile shale or phyllite, varying in color from grayish green or 



*Geol. Surv. Rhode Island, 1840, pp. 89-92. 



f E.' Hitchcock, Geol. Mass., 1841, pp. 5H7-552. 



JGeol. Is. Aquidneck, Proc. Am. Ass. Adv. Sci., 1860, pp. 119, 121, 126. 



§ Proc. Bost. Soc Nat. Hist , vol. xiv, 1869. 



[Proc. Bost. Soc. Nat. Hist., vol. xxii, p. 179, 1883. 



\ This Journal, vol. xxvii, 1884, pp. 217-226, 282-291. 



