AN OUTLINE REVIEW OF THE GEOLOGY OF PERU. 
[With 5 plates.] 
By GerorcE 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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