AN OUTLINE REVIEW OF THE GEOLOGY OF PERU. 



[With 5 plates.] 



By Geoege I. Adams. 



Introduction. 



More than a century has elapsed since Humboldt beheld the grand 

 Cordilleras in northern Peru, and more than three-quarters of a cen- 

 tury has passed since d'Orbigny studied the section of the Andes in 

 the southern part of the country. Since then many scientists have 

 been attracted to the region and have contributed to the knowledge of 

 its geology. Their writings are scattered in numerous publications 

 in English, German, French, and Spanish, and no summary of this 

 information has been made. The writer in attempting to learn what 

 is known concerning the subject has gleaned the material which con- 

 stitutes this paper. The arrangement and presentation of it in the 

 form of an outline review has been undertaken with the hope that it 

 may serve as an introduction to the broader problems with which 

 later geologists may have to deal. 



The author's contributions to the geology of Peru have been pub- 

 lished in bulletins of the Corps of Engineers of Mines of Peru, and 

 relate principally to the distribution of the Tertiary formations of 

 the coast of which he made a reconnaissance. Later, while engaged 

 in private work, he traveled in the Titicacan region of Peru and 

 Bolivia, crossed the Cordilleras, and entered the forest region of 

 southern Peru, and also saw something of the Cordilleras of the 

 central part of the country. It is not his intention, however, to at- 

 tempt to incorporate his observations during these journeys to any 

 great extent in this paper, but rather to use them as an aid to the in- 

 terpretation of the work of others. 



The geologic relations of the rocks of Peru have thus far been ex- 

 plained by written descriptions accompanied in some cases by sections, 

 but there are practically no geologic maps. It is to be hoped that 

 the mapping of some type localities may soon be undertaken and that 

 the columnar sections for the various regions may be established 

 and the paleontologic studies correlated with them. The time has 

 arrived when simple geologic reconnaissance can not be expected to 

 yield satisfactory results. 



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