\j Jul J\. X X Sju S\i XX* 



THE PRE-CAEBONIPEEOUS EOCKS. 



ALGOKKIAN FEKIOB. 



BLACKSTONE SERIES. 



Primary (limestone and hornblende rock). C. T. Jackson: Report on the Geology and Agriculture of 



Ehode Island, 1840. 

 Tacouic fStockbridge limestone, etc.). E. Emmons : Agriculture of New York, Vol. 1, 1846, pp. 90-93; 



also American Geology, Vol. 1, 1855, p. 22. 

 Montalban. W. 0. Crosby : Geology of Eastern Massachusetts, 1880, p. 128. 

 Pre-Cambrian (Huronian?). N. S. Shaler: Bull. Mus. Comp. Zool. Harvard Coll., Vol. XVI, 1888, 



pp. 15-18. 



The above-named writings, with their chronological references, as 

 made at the date of the respective papers, set forth in a word the views 

 advanced regarding the age of the series of limestones, chloritic and horn- 

 blendic schists, slates, and quartzites, which occur in the lower portion of 

 the Blackstone Valley and near Providence, within the limits of Ehode 

 Island, along the western border of the Carboniferous basin. It evidently 

 has been the common opinion of geologists that these rocks are older than 

 the Paleozoic series The names here introduced, without a geological 

 map, are intended as locality terms only. 



The Carboniferous strata of this basin rest everywhere unconformably 

 on older rocks, which are found immediately bordering the basin or as 

 small inliers within its limits. These inliers are Cambrian sediments, with 

 associated igneous rocks. The pre-Cambrian or Algonkian rocks above 

 referred to as the Blackstone series occur in the form of highly inclined 

 masaes of strata separated and penetrated by granitic intrusions or bath- 

 olites. The area of these clastic and the associated igneous rocks, now 

 exposed at surface along the western border from Cumberland southward 

 in Ehode Island, is about equally divided between the two groups. The 

 thorough disruption of these ancient strata by changes of attitude and 

 igneous intrusion has produced in the area a type of structure which may 



104 



