GEOLOGY AND PALEONTOLOGY OP THE CANAL ZONE. - 295 



This examination reveals three kinds of limestone, the uppermost 

 of which subsequently may be subdivided. The three divisions are 

 as follows: 



Specimens 1-4 (0-241 feet) represent a limestone which is largely or 

 mostly of organic origin, but which may contain a few grains of 

 chemically precipitated material. This corresponds to the upper 

 faunal division recognized by Cushman. 



Specimens 5-7 (241-341 feet) represent a pulverulent limestone, 

 composed of rounded grains imbedded in finely crystalline material. 

 The grains in their size and shape resemble oolite, and some grains 

 showed with greater or less distinctness suggestions of oolitic struc- 

 ture. The foraminiferal fauna is meager, but it differs from that of 

 specimens 1-4 and the underlying bed represented by specimen 8. 

 It seems safe to draw the inference that this division of the lime- 

 stone is in part, at least, a chemical precipitate. 



Specimen 8 (341-383 feet) represents an impure, foraminiferal, 

 earthy limestone, or a calcareous marl, in which there may be some 

 chemically precipitated material. This bed is the uppermost in 

 which the Nummulites reported by Cushman occur. It was also 

 found in the underlying bed No. 9, 383-393 feet. 



Probable geologic age of the limestone in the Bermuda well. 



[Height of well mouth above sea level, 135 feet.] 

 Samples. Probable geologic age. 



From 1-241 feet Recent and Pleistocene. 



From 241-286 feet Pliocene or Miocene. 



From 331-341 feet Nothing determinable. 



From 341-393 feet Oligocene or Eocene (Nummulites). 



From 393-485 feet Eocene? (no Nummulites). 



An outline of the geologic history of the Bermudas subsequent 

 to the volcanic activity seems to be as follows : 



Doctor Cushman's identification of the Foraminifera from the 

 Bermuda well shows the presence of an undetermined species of 

 Polystomella between 393 and 480 and between 480 and 485 feet. 

 These depths are well down in the oxidized zone and indicate marine 

 conditions which persisted throughout the deposition of the super- 

 incumbent material. Other Foraminifera occur between 383 and 393, 

 one of them being a species of Nummulites, which was also obtained 

 from the basal bed of limestone at a depth of 341 feet. As the 

 genus Nummulites is, according to our present knowledge, confined 

 to the upper Eocene and Oligocene formations in the southeastern 

 United States and the West Indies, the inference may be drawn that 

 the Bermuda samples between 341 and 393 feet probably represent a 

 geologic formation of either Eocene or Oligocene age, and that those 

 from 393-485 feet represent a formation of probably Eocene age. 

 37149— 19— Bull. 103 8 



