M, Howe — Geology of the Isthmus of Panama. 219 



cally all the way from near San Pablo to the type locality at 

 Bas Obispo. Hill noted the presence of these conglomerates 

 at the places named and correlated them with the beds at the 

 Bohio lock site.* 



Vamos Vamos and Gatun beds. — About two and a 

 half miles west of Bohio, on the south bank of the French 

 canal, at a locality known as Yamos Yamos, are exposures of 

 sedimentary rock that have been described by Hillf and Ber- 

 trand.if The rocks are impure calcareous shales or marls of a 

 dirty brown color, rich in fossils, and at certain horizons con- 

 tain numerous large fossiliferous calcareous concretions that at 

 first suggest bowlders in a conglomerate. 



Following the line of the French canal northwest for nearly 

 six miles, no outcrops of any sort are to be seen until within a 

 short distance of Gatun, where, on the left bank of the canal, 

 are exposures of extremely fossiliferous marls and calcareous 

 sandstones. Similar beds are exposed along the cuttings of 

 the Panama Railroad through Tiger Hill between Bohio and 

 Gatun. No other exposures in this region are known, but a 

 great number of borings made at Gatun in exploration of dam 

 and lock sites furnish much valuable imformation in regard to 

 the character of the rocks. The samples of borings from the 

 lowest sedimentary rocks at Gatun are all of extremely fine- 

 grained, even-textured sandstones which in some places merge 

 into sandy shales. The cementing material is usually calca- 

 reous, but considerable earthy impurity or clay is often present. 

 The coarser components of the rock at Gatun and of that occur- 

 ring along the canal between Gatun and Bohio consist of 

 igneous material ; in many specimens grains of nearly fresh 

 feldspar and ferro-magnesian silicates may be recognized, but 

 as a rule the material is in such a finely divided state that it is 

 impossible to say whether it is of direct volcanic origin or has 

 resulted from the degradation of older igneous rocks. At 

 many points fossils are abundant in the core specimens and 

 carbonaceous matter is very generally present. 



Age of the Bohio formation.. — From fossils collected by 

 Hill and others and by myself and examined by Dr. William 

 H. Dall, it appears that the beds described are of Eocene age 

 and contain a number of species typical of the Claiborne and 

 some common to the Upper Tejon of California.§ In the 

 material that I collected at Yamos Yamos Dall has identified 

 the following species : 



*Op. cit., 188. fOp. cit., p. 179. {Op. c it., p . 6. 



§Hill, op. cit., Part VI, Report by Dr. William H. Dall upon the Paleon- 

 tology of the collections, pp. 271-275. 



