NORTH AMERICAN GEOLOGY 221 



western California are colored. McGree's map is dated 1884, and is not 

 only compiled from published information, but from manuscript maps in 

 some areas. It differs from previous maps in numerous respects. Besides 

 more accurate delineation of boundaries, the crystalline rocks of New 

 York Island and of Westchester County are represented as Silurian ; the 

 New England crystallines and those of all the Piedmont and Appalach- 

 ian belt are colored as Archean, including the semi-crystalline schists of 

 central South Carolina, central and western North Carolina, south- 

 eastern Pennsylvania, and parts of New England. The oldest rocks of 

 Texas are referred to the Cambrian, and the Archean area in Missouri 

 are shown surrounded by Cambrian. The southern half of Long Island 

 is represented as Tertiary, and much of the Atlantic coast, especially 

 that of North Carolina, is thus shown. The gypsiferous series of Kan- 

 sas, Indian Territory, and New Mexico is incorporated with the Creta- 

 ceous; the Eocene of Texas is given a great width along the Rio Grande ; 

 the cross-timber district of Texas is shown as Quaternary, and a large 

 portion of Dakota and Minnesota is similarly shown. 



95. Hitchcock copies McCee's boundaries in districts of which the 

 geology is less open to question. In the Black Hills and eastward the 

 Archean is subdivided into Laurentian and Huronian. Cambrian is 

 represented in southwestern Maine, in central South Carolina, and in 

 west central and in western North Carolina. Th^e underlying rocks 

 are shown as far as possible in Minnesota and Dakota instead of the 

 overlying drift, information for Minnesota having been furnished by 

 TTpham. The gypsiferous series of Indian Territory, Texas, and New 

 Mexico is shown as Trias, and the Jura and Trias are separated as far 

 as possible in other parts of the West; much information from Pum- 

 pelly, Blake, Willis, Dutton, and Diller is utilized for the far West, 

 but large areas are colored hypothetically. The gold slates of California 

 are represented as Jurassic and Cretaceous metamorphic, but not with 

 approbation. For the Canadian areas in the East and far West much 

 new information has been incorporated. 



During the past year there has appeared the report of the Interna- 

 tional Congress of Geologists, in which an account is given of the re- 

 sults attained towards uniformity in geologic nomenclature and cartog- 

 raphy. 



PETROGRAPHY. 



Besides the papers referred to in the following paragraphs, there are 

 several others containing petrographic information of a most interest- 

 ing character, notably those of Becker on the Cretaceous crystallines 

 of California, and Williams on a district west of Baltimore, both of 

 which are noticed under " Metamorphism and Paramorphism." 



96. G. H. Williams describes in detail the petrographic characteris- 

 tics of the peridotites of the Cortlandt series near Peekskill, New York. 

 Two varieties are found, one containing hornblende and the other py- 



