194 L. V. Pivsson — Geology of Bermuda Island ; 



The various facts which are embodied in the foregoing table, 

 together with those covering the dimensions of the boring, 

 may be graphically shown in the accompanying figure (tig. 1). 

 From this it is easy to see that the boring has penetrated three 

 zones of essentially different materials, the natures of which 

 are indicated on the side of the diagram, as follows: first, 

 the soft chalky Bermuda limestones ; second, a layer of soft oxi- 

 dized volcanic matter, yellow to brown in color; and third, 

 firm compact lavas, dark gray in color, which persist to the 

 bottom of the well. Each of these three zones has been 

 found to have particular features of its own, which when 

 subjected to study have proved to be of interest in throwing 

 light on the geologic history of the island. That of the first, 

 the chalky limestones, has yielded information concerning the 

 work of organic life and the more recent phases of that history. 

 The study of the oxidized and unoxidized layers of volcanics, 

 with the conclusions to be drawn from them, will be given in 

 the following part of this paper, and there is appended the 

 results of a petrographic investigation, carried so far as the 

 nature of the material permitted. 



Zone of Oxidized Material. 



This extends from where the Bermuda limestone ends down 

 to about 600 feet below the surface. Its general color is a 

 leather brown varying from a pale buff-yellow to dark brown. 

 In some cases the inner portion of fragments is a brownish- 

 gray to lead-gray. In the sample taken at 573-574 feet the 

 color is quite different, a dark blackish-gray ; on either side of 

 this thin layer the regular brown color obtains and its signifi- 

 cance will be discussed later. 



All the samples consist of a mixture of sand or earthy 

 powder, mingled with fragments, which in some cases are as 

 large as hickory nuts. The material is soft; in some cases it 

 can be readily rubbed between the fingers, in others it is not so 

 friable but can be easily cut or scraped with the finger-nail ; 

 the hardest pieces can be readily cut with a knife. 



The series begins with a very fine-textured material of a 

 buff color, which is in altered lava ; some small white specks 

 in it may be decomposed phenocrysts. This is succeeded from 

 393-485 feet by fragmental material which is very evidently a 

 decomposed amygdaloid. The larger pieces still retain the 

 amygdaloidal structure and are filled with amygdules the size 

 of fine shot ; mingled with the debris of this are many larger 

 separated amygdules of calcite. From 485-518 feet the mate- 

 rial is different ; the amygdaloidal structure is wanting, the 

 fragments are of a fine dense texture, and are evidently a highly 



