REVIEWS 269 



It is obvious that there are large breaks in the sequence, due either to 

 lack of knowledge or to unconformities. Both conditions exist. Geo- 

 logic history is meagerly recorded in the great plateau of Brazil, which, 

 in many respects, closely resembles the Laurentian Plateau of Canada 

 and its marginal areas. Our knowledge of the record as far as it exists is 

 also very incomplete. 



The author says: 



In view of the limitations of our knowledge, it is not possible to represent 

 on the map more than thirteen subdivisions of the geologic column. In some 

 localities many more subdivisions are known and, over a limited area, might 

 have been shown, but there would be no particular object in giving all of these 

 subdivisions on a map of this scale. The minor details, even where they are 

 known, are necessarily omitted on account of the small scale of the map. In 

 regions of horizontal rocks, where partings are dendritic in form and outliers are 

 abundant, these features cannot conveniently be shown. The areas of old 

 crystalline schists are almost everywhere traversed by dikes of eruptive rock, 

 but these dikes are usually too small to be shown on the map of the scale of this 

 one. The same thing is true in the southern states, where numerous dikes cut 

 all of the rocks below the Cretaceous. 



The degree of generalization in classification in the map of Brazil is 

 similar to that of McGee's geologic map of the United States (1884), but 

 only a small portion of the map of Brazil is based on detailed topographic 

 and geologic surveys like those which were available to McGee. Rather 

 might we compare Branner's map with that of the United States by 

 Marcou (1853)^ or by Hitchcock and Blake (1874).^ Dr. Branner 

 himself has expressed the opinion that the geology of the United States 

 was better known when Marcou published than is that of Brazil today. 

 Branner's map is, however, far superior to Marcou's as a work in cartog- 

 raphy, because of its rigid adherence to known facts, although it cannot 

 be compared with Hitchcock's from the point of view of completeness of 

 knowledge. 



Judging by these criteria it is reasonable to state that knowledge of 

 the geology of Brazil is more than half a century behind that of the 

 United States. To a certain extent this may be attributed to physical 

 difficulties, tropical vegetation, soil covering, and the general absence of 

 fossils. But a more potent cause is the lack of general interest among 



'Jules Marcou, "Resume explicatif d'une carte geologique des Etats Unis et des 

 provinces anglaises de rAiiierique du Nord, etc.," Bull, de la Soc. Geol. de France 

 Second Series, Vol. XII, 1854-55. 



^^C. H. Hitchcock and W. P. Blake, Geologic Map of the U.S. in Statistical 

 Atlas, Ninth Census, 1874. 



