158 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



As far as known, the pre-Cambrian is only exposed in the north 

 and on the Argentine side of the Bolivian high plateau. 



COLOMBIA AND ECUADOR. 



The work of W. Sievers, A. Hettner, A. Stuebel, and Theodore and 

 W. A. Wolf permits a general view of the geology of these countries. 

 As already emphasized, the Andes of Colombia, divided into three 

 chains, do not continue toward the Isthmus, but bend eastward 

 toward Venezuela. The coast, both in Colombia and Ecuador, is oc- 

 cupied by Tertiary strata. The Cordilleras consist in general of a 

 core of crystalline schistose rocks which are generally referred to the 

 pre-Cambrian. Above these there is a great break in both countries : 

 The Paleozoic and the early Mesozoic apparently are missing. In- 

 stead, the Cretaceous overlies the schists and the extensive beds are 

 divided into the Lower and Upper, the latter being overlain by the 

 Guaderas beds, probably also Cretaceous. There was no marked 

 folding during the Cretaceous. Quartz monzonites and allied rocks 

 are reported from many places; they are older than the Tertiary and 

 younger than the Upper Cretaceous. Flows of " labradorite porphy- 

 rite" and tuffs are embedded in the Cretaceous. 1 



The Cretaceous is unconformably overlain by the Tertiary. La- 

 tites and tuffs represent the volcanic activity of the early Tertiary, 

 continued by the ejectamenta of a series of recent volcanoes, most 

 strongly represented in Ecuador. 



A sketch map of the general geology of Ecuador, by W. A. "Wolf, 2 

 shows similar conditions. There is a broad belt of Tertiary beds 

 along the coast adjoined by a narrow belt of Cretaceous with as- 

 sociated eruptives. Then follows the volcanic belt, Quito being 

 placed at its eastern margin, and the main cordillera east of that 

 city is built of granite and crystalline schists, all probably pre- 

 Cambrian. 



Much information on the geology of Peru is contained in the pub- 

 lication of the Cuerpo de Ingenieros de Minas at Lima, which include 

 also some of the important writings of Prof. G. Steinmann. The 

 results refer mainly to the western and central cordillera, and the 

 geological features of the Montana slope, clad in tropical vegetation, 

 are as yet little elucidated. 



1 E. Lehmann : Beitrage zur Petrographie des Gebietcs am oberen Rio Magdalenn 

 (Tschermak's Mineralogische u. Petrographische -Mitteilungen, vol xxx, pp. 233 to 280 

 (1911)). 



2 Sketch of the Geology of Ecuador (condensed in Mining and Scientific Press, vol. cv. 

 No. 4 (July 27, 1912)). 



