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XV. The Geological Age of the Mountains of Santa Marta. 

 By Professor Hermann Karsten, M.D.* 



THE Geological constitution of the mountain-mass of 

 Sta. Marta has until recently remained quite unknown. 

 It was only in consequence of my Report of 1852 upon " The 

 neighbourhood of Maracaybo and the North coast of New 

 Granada" (Karsten's Archiv, 1853), in which the geological 

 age of these mountains was touched upon, and after the pub- 

 lication of the nearly simultaneous investigation of this region 

 by Acosta {Bull, Soc. Geol. Fr. ser. 2, vol. ix. p. 396, June 

 1852), that these questions have been dealt with more in detail, 

 both in my subsequent geological writings and in those of my 

 successors. 



Acosta, like myself, describes the Geological constitution of 

 the Sierra Nevada de Sta. Marta as Plutonic, consisting of 

 Granite, Gneiss, Syenite, Diorite, Eurite, &c, and of Porphyries 

 traversed by veins of malachite. Neptunian strata, from 

 which the age of the mountain-mass might be inferred, are 

 not cited by Acosta ; but he concludes, from the complete 

 isolation of the massif, and from its East and West direction, 

 that it existed long before the upheaval of the Cordillera, 

 which runs North and South. 



In my discourse upon "The Geological Constitution of 

 New Granada" {Amtlicher Benefit der Versammlung cler 

 Naturforscher, 1856, Vienna 1857) I also describe the Sierra 

 Nevada de Sta. Marta in more detail as a distinct mountain- 

 system which abuts with its south-eastern declivity upon the 

 chain of Ocana striking northward from Bogota, and by sub- 

 sequent upheavals there was united therewith by means of a 

 narrow and low connecting range (p. 81). This mountain- 

 mass of Sta. Marta consists of alternating beds of crystalline 

 rocks : — Granite, Gneiss, Protogine, Syenite, Hornblende-, 

 Chlorite- and Quartz-schists, — which have a general strike 

 from S.W. to N.E. In the periphery of this formation there 

 are readily weathering Diorites, Porphyries, Syenites, Gra- 

 nites, &c. Towards the east and south-east beds of the 

 Cretaceous formation bound these rocks, a continuation of 

 those which compose the mountains of Ocana (Perija). The 

 lowest of these Neptunian beds is a red sandy laminated marl 

 in which Ammonites santafecinus, D'Orb., occurs, and which 

 alternates upwards with dark, bituminous limestones and 

 siliceous schists containing Ammonites and Inocerami. These 

 are covered by light-blue limestone-beds, in which Ed'ogyra 

 * Communicated by the Author. 





