6 INDEX TO THE STEATIGRAPHY OF NORTH AMERICA. 



The Canadian Survey has issued two bibliographies, ^^' "* which were very 

 useful. In them subjects may readily be traced by locality, geologic division, or 

 geologist. 



For North American geology prior to 1892, the bibliography by Darton ^^ has 

 been used. 



In addition to published material, the compiler has been freely given a very 

 large amount of unpublished information from the records of the United States 

 Geological Survey. Some has been taken from oflEicial manuscripts and some from 

 notes prepared for this paper. All this material is credited in the text and in the 

 list on pages 30-61, which shows the names of the contributors and the localities 

 'which they have described. 



ARRANGEMENT OF MATERIAL. 



The material assembled has been arranged arbitrarily according to the index 

 of the map, in order to facilitate reference between the map and the text. Natural 

 divisions and systematic classification have thus been subordinated to convenience. 



The map is divided by parallels at intervals of 4 degrees and by meridians at 

 intervals of 6 degrees, according to the plan of sheets of the Standard International 

 Map of the World. Any space thus inclosed is designated by a letter and a number. 

 The letters run from A at the equator to V at the pole, and may be said to designate 

 zones. For example, zone A is bounded by the equator on the south and by the 

 parallel of 4° north latitude on the north; zone H includes northern Mexico and the 

 Gulf coast of the United States; zones L and M are traversed by the boundary of 

 the United States and Canada; zones P, Q, and R comprise Alaska, northern Canada, 

 and southern Greenland. 



The spaces between meridians are numbered from west to east, from longitude 

 180° to Greenwich. In accordance with the usage of European cartographers, 

 these spaces may be called columns. Alaska falls in columns 3 to 7. The eastern 

 United States, Quebec, and the Labrador Peninsula lie in columns 18, 19, and 20. 



The letter and number which designate the zone and column in which any 

 division of the map lies define the position of that division and may be employed to 

 designate it. For example, division L 18 comprises the St. Lawrence from Lake 

 Ontario nearly to Quebec; J-K 13 covers the Rocky Mountains of Wyoming and 

 Colorado; and E 14 takes in the City of Mexico and vicinity. The index divisions 

 are employed throughout this work to designate areas. 



The division into chapters is based on geologic divisions and in general each 

 chapter corresponds with a geologic system or period defined by the current usage 

 of the United States Geological Survey and named in the legend of the map, but 

 there are departures from a systematic classification which arise partly from the 

 exigencies of cartography and partly from the inaptness of standards. These 

 departures are stated below, in the legend of the map, and in connection with each 

 chapter also. 



The order of description follows the alphabetical and numerical sequence — that 

 is, from B 17 to B 20, then from C 16 to C 20, etc., wherever the outcrops of strata 

 or the svstem under consideration occur. Each zone is followed from west to east 



