200 I. V. Pirsson — Geology of Bermuda Island ; 



were also probably covered with more or less loose debris 

 which would be first attacked by the waves and fed to them 

 by the drainage, would give place to more solid, resistant lavas, 

 and with increasing progress to thicker and thicker masses. 

 The rate of erosion would then be, comparatively, greatly 

 retarded, and the action of the atmosphere would have time to 

 make itself felt upon the material of the land surface before it 

 was eroded by the waves and buried under the sea. Conse- 

 quently, we should expect the deposit from then on to exhibit 

 the oxidation characteristic of land waste, which is, in fact, the 

 chief feature of the samples from 590 feet up to 380 feet, 

 where the limestones begin. 



In the history, however, thus briefly sketched two episodes 

 occurred, which are of interest in this connection and should 

 not be forgotten. It relates to samples numbered 38 and 18. 

 Number 38 is from a depth of 1,045 to 1,075 feet, and, while 

 much of it is splintery rock broken by the drill, it also contains 

 a large proportion of neatly-rounded water-worn grains of lava, 

 some of which are more or less weathered, together with small 

 specks of red oxidation products of iron ore. This must repre- 

 sent one of the earlier stages of the emergence of the growing 

 volcano above the sea and the attack upon it by the waves. 

 As in the higher level at 700 feet, mentioned above, there was 

 no serious or deep weathering before the material was washed 

 out and deposited on the lower slopes of the volcanic mass 

 beneath the water. This was then covered by fresh outflows 

 of lava as the formation of the cone continued. 



In a similar manner the tnin layer of number 18, 573-574 

 feet, which consists of unoxidized blackish material in the 

 midst of the weathered land-waste, indicates a renewal of vol- 

 canic activity and the wearing and washing down of this new 

 volcanic product. It may, therefore, represent the last out- 

 break that occurred before the volcano became extinct. 



Tuffs and Breccias. — An important feature of the discus- 

 sion of the Bermuda volcano is the question whether it was 

 wholly a lava cone or a mingling of flows with tuffs and 

 breccias. This problem, obviously, cannot be definitely 

 answered. So far as the evidence goes no tuffs or breccias, it 

 is thought, are indicated. Certainly from 700 feet down the 

 samples w 7 ith one exception appear to be merely those of 

 crushed, solid rock. If the boring had been made by a diamond 

 drill with the production of a solid core it would be of course 

 much easier to determine whether tuffs and breccias were 

 present, through the section given us by the well. The pound- 

 ing up of the rocks by the churn drill makes it much more 



