the Igneous Platform. 205 



shown with a total thickness of TOO feet. The average thick- 

 ness would be of course 100 feet for each flow, which is not 

 excessive, but one would be 150 feet. There were probably 

 more flows than this, some of which were not amygdaloidal at 

 the top and which could not, therefore, be differentiated in the 

 crushed rock of the samples; and this is indicated by petro- 

 graphic variations within single samples. In general it is noted 

 that the lava of the upper part of a flow is denser and darker, 

 giving way to lighter colored, lead-gray, less compact material 

 below. 



Mr. Howe's notes show that in two places, after the lava in 

 place was penetrated, salt water entered the well. These 

 places, as the section shows, are at points between lava flows 

 and thus a natural place in which to expect it. For along such 

 surfaces of contact and especially on account of the porous, 

 vesicular, broken nature of the upper part of the lower flow, 

 the water would be able to penetrate rather than through the 

 solid middle portion of a flow. 



Geological Age of the Volcano. — The identification of the 

 foraminifera from the Bermuda well by Doctor Cushman and 

 the study of the calcareous deposits by Doctor Vaughan have 

 led the latter, in a communication which he has kindly sent 

 me in advance of his own publications, to assign the Eocene, 

 or lower Oligocene, as the time when they began to accumu- 

 late on the submerged volcanic basement. The submergence 

 progressed until the basement, in, probably, Miocene time, was 

 entirely blanketed by calcareous deposits 100 feet thick. He 

 feels, therefore, that it appears safe to assign an Eocene, or 

 pre-Eocene, age to the Bermudian volcanic activity. The 

 great size of the extrusive mass has been previously described 

 and to accumulate this huge pile a period of time, long perhaps 

 even from the geologic standpoint, must have been required 

 and another long interval to cut away completely the island 

 masses and reduce them to the platforms that now exist. 

 Verrill* suggests that the volcano was completed or formed 

 daring the Triassic or at its close and correlates it with the 

 igneous outflows which characterized this period along the 

 North American coast. It may indeed date from this time, 

 but it should be observed that the diabases of the Triassic are 

 a feature of the border of an entirely different earth-segment 

 from the one on which the Bermuda volcano is situated, one 

 which has had a very different geologic history, and that they 

 made their appearance while the region was undergoing tec- 

 tonic movements of which we have no knowledge in the Ber- 

 muda area. We have indeed no direct way of knowing the 

 period in which volcanic activity has begun in the case of sub- 



* Op. cit. p. 53. 



Am. Jour. Sci.— Fourth Series, Vol. XXXVIII, No. 225.— Sept., 1914. 

 15 



