the Igneous Platform. 201 



difficult. It seeins fairly safe to say, however, as mentioned 

 above, that none are present from TOO feet down. It is also 

 thought that the samples from this point up are composed 

 wholly of the oxidized waste of lavas similar to those lower 

 down. The reason for this belief is that where these samples 

 contain fragments which are obviously not chips broken by 

 the drill but are, so to speak, automorphic, as many of them 

 are, such fragments do not appear like lapilli. They are very 

 prevalently fragments of an amygdaloid or of solid lava, often 

 smoothly rounded, as if by beach rolling, as described above. 

 Amygdaloid may occur among breccias, but it is certainly 

 much more characteristic of the upper part of lava flows. Xo 

 pieces having an empty vesicular structure have been observed. 

 Judging from these facts, it is thought that the balance of evi- 

 dence points to the absence of the products of explosive vol- 

 canic activity. Moreover, the very basic, basaltic nature of 

 most of the lavas, which is shown later under their petro- 

 graphic description, agrees with this idea, for the magmas 

 which furnish such rocks are usually very "fluid and their dis- 

 charge, as is well known, is far less apt to be attended with 

 explosive phenomena than more siliceous felsic ones. 



If it be true, then, that the Bermuda volcano is mainly or 

 wholly a lava cone as indicated, this would have an important 

 bearing on the topographic form of the original island, from 

 the fact that lava cones are relatively rather flat with low 

 angles of slope, compared with tuff and breccia cones, which 

 are steep and high. 



Form and size of the Bermuda Volcano. — Bermuda Island 

 has been thought to be situated upon the apex of a volcanic 

 mountain mass, and Verrill* has made some suggestions as to 

 its size, slopes, and probable history, but until the present bor- 

 ing was undertaken, there have been no direct facts which 

 would prove this. Other than the statements and suggestions 

 of Verrill, so far as the writer is aware, there has been no 

 attempt made to consider its form and size in this connection. 

 It would seem of interest to do this to obtain some data for 

 comparison with other volcanic masses of a similar nature and 

 situation. 



Alexander Agassizf has given a partial profile of Bermuda 

 running in a northeast and southwest direction and slightly 

 bent, so that it passes through the greatest length of the island 

 and then through the Argus and Challenger Banks to the 

 southwest. In this profile the vertical scale is much exag- 



* Bermuda Islands, Pt. IV, Geology and Paleontology, Trans. Conn. Acad. 

 Arts and Sci., vol. xii, 1907, p. 55. 



f Visit to the Bermudas in March, 1894, Bull. Mus. Comp. Zool., vol. xxvi, 

 No. 2, 1895. 



