384 REVIEWS 



Summary Report of the Geological Survey Branch of the Department 



of Mines, Canada, for the Calendar Year igog. By R. W. 



Brock, Director. Pp. 307. 



Besides the administrative report of the director of the survey, 



there is included in this volume a short summary report by each of the 



geologists and officers of the survey, of the work carried out during the 



year. Almost all of the work at present being undertaken is along 



economic lines. 



E. R. L. 



"The Tectonic Lines of the Northern Part of the North American 

 Cordillera." By W. Joerg. Bull. Am. Geog. Soc, XLII 

 (1910), 161-79. With map. 



This paper pictures the tectonic lines of the North American Cor- 

 dillera from the 40th parallel to Bering Sea. Though the author has 

 based his work in part upon the reports of the geological surveys of the 

 United States and Canada, he has confessedly followed Suess, in the 

 main, both in subject-matter and in mode of treatment. The chief 

 purpose of this paper is to consider in their larger relations the individual 

 ranges and groups of ranges which go to make up this complex system. 

 The interrelations of these mountain chains are discussed in a condensed 

 synoptical form. The axes of the many separate, individual ranges 

 are located on the map by heavy black -tectonic lines which show graphi- 

 cally the distribution and direction of deformative movements. A 

 prominent place is given to the mountain systems of Alaska. 



In conclusion the author suggests the subdivision of the North 

 American Cordillera from Bering Sea to the Isthmus of Tehuantepec 

 into three major divisions: (1) Northern Cordillera, or Alaskides; (2) 

 Central Cordillera; (3) Southern Cordillera, or Lower California and 

 the Mexican Highland. 



The boundary between the first and second divisions would be the 

 zone of coalescence near the Alaskan boundary, that between the second 

 and third the depression along Salton Sink, the Gila, and the Rio Grande. 

 The decided Asiatic structure of the Alaskides is the reason given for 

 recognizing them as an independent major subdivision of the Cordillera. 



R. T. C. 



