118 ABSTKACTS: GEOLOGY 



gypsiferous and saline clays to part of the Maccrady formation is 

 discussed. The various theories that have been offered to account for 

 the accumulation of these deposits are described. The fact that the 

 deposits are found only close to the fault and are not known to occur 

 in quantity in the same strata any distance away from the fault, leads 

 the author to the conclusion that disseminated salt and gypsum in the 

 original sediments of earthy limestone, shale, and sandstone, have been 

 concentrated in the same strata adjacent to the fault by circulating 

 waters thru chemical affinity. The ammonia-soda process, which is 

 used in converting the brine of these wells into soda products is 

 described. G. W. S. 



GEOLOGY. — Index to the stratigraphy of North America. Bailey 

 Willis. Accompanied by a geologic map of North America, com- 

 piled by Bailey Willis and G. W. Stose. Professorial Paper 71, 

 U. S. Geological Survey. 1912. 

 This, report summarizes what are regarded as the most authoritative 

 statements concerning the geology of the North American continent. 

 The map, 60 by 77 inches, to which the text is an extended key, is 

 printed in 4 sheets which are folded and encased in a separate box. 

 Its scale is 1 : 500,000 or approximately 1 inch to 80 miles. The 42 

 color distinctions represent as many divisions of strata. There are 

 distinguished 6 main divisions of the pre-Cambrian, 7 of the Paleozoic, 

 6 of the Mesozoic, and 7 of the Tertiary. Besides these main divisions 

 larger equivalents in parts of the continent, where details are not known 

 or are too minute to be mapped, are represented by distinct color effect. 

 The color scheme is planned so that the map fulfills two purposes — 

 that of a wall map and of a pocket map. Viewed on a wall only the 

 larger units and the different geologic provinces stand out. The Cana- 

 dian shield of pre-Cambrian rocks for example is set off sharply from 

 the parallel bands of Paleozoic rocks of the Appalachians, and the lava 

 fields of the western states from the Mesozoic and Tertiary rocks of 

 the Great Plains and the older rocks of the Rocky Mountains. At 

 close range, on the other hand, the more minute subdivisions can readily 

 be distinguished. 



To facilitate references in the text, the map is divided into rectangu- 

 lar spaces, each embracing 4 degrees of latitude and 6 degrees of longi- 

 tude, which are designated by letters and numbers. The text is closely 

 linked to the map by these coordinates, which form the basis of the 

 arrangement of the quotations. Except the explanatory matter in the 

 chapters on introduction and bibliography the descriptions are arranged 



