386 Rev. R. Ashington B alien — 



some new facts to record, and nothing has yet appeared in the 

 Geological Magazine on the geology of Bermuda, a paper may be not 

 altogether out of place. 



In February last, when I told him of my intention to visit 

 Bermuda, our veteran authority on the physics of the earth's crust, 

 the Rev. Osmond Fisher, wrote : " The Bermudas are, I think, 

 entirely volcanic. But I suppose quite anciently so, and that there 

 are no cones, etc., now. There must be some interesting questions 

 connected with them regarding changes of level of the ocean bed." 

 Mr. Fisher was, of course, referring to the substratum of the islands. 

 The evidence for the vulcanological origin of that proto-Bermudian 

 land is threefold. 



(a) Charting. There is the evidence of the Admiralty charts. In 

 the narrative of the cruise of the Challenger 1 we find that the 

 distance of 6 miles from the reef edge on the north-west of the group 

 gave a sounding of 1,370 fathoms, and at 10 miles 2,100 fathoms. 

 The slope off the North Bock is steeper than that off the north-east of 

 Castle Harbour, e.g. : 



Slope off North Rock 1,370 f. at 6 miles distance from reef edge. 

 Castle Harbour 1,250 f. at 8 miles from the 100 f. line. 

 ,, south-west of Long Bar 1,250 f. at 5 miles from the 100 f. line. 

 ,, north-east of East Ledge 1,000 f. only 2 miles from the 100 f. line, 



and 1,260 f. at 5\ miles from the 100 f. line. 

 ,, south-west of the South-West Breaker 960 f. only 2 miles from the 

 100 f. line, 

 off the Argus Bank 1,370 f. at 10 miles from the 100 f. line. 



This sudden deepening of the underlying mountain of which Bermuda 

 is the summit, with two submerged peaks called the Challenger 

 and Argus Banks respectively to the south-west of Somerset, is in 

 accordance with the steep slope of a volcano with three peaks. The 

 present degraded Bermuda volcano has a height of about 15,000 feet, 

 equal to Mont Blanc. 



(b) Magnetic Deflection. General Lefroy, Governor in the seventies, 

 found that his own observations did not agree with the Admiralty 

 charts. Observations made by the Challenger Expedition showed 

 a variation of 6° in various parts of the islands, ranging from 4° W. 

 to 10° W., the smallest amount being found at a small islet under 

 Gibb's Hill and the greatest at the point west of Clarence Cove. The 

 disturbing cause is probably the existence of iron rocks within 

 varying depths from the present surface. 



(c) Analogy. The well-known volcanic character of the Madeiras, 

 Azores, Canaries, and other islands and rocks in the Atlantic would 

 argue a similar origin for the Bermuda group. The islands mentioned 

 are of Tertiary date, 2 but it is impossible to state the date of the 

 Bermudas under present evidence. Verrill correlates them with 

 Martinique and the West Indian group. Speaking of the main mass 

 and also of the Challenger and Argus Banks he says, " No doubt each 

 of these peaks and craters when they were most active rose high 



1 Wyville Thomson, Voyage of the "Challenger", vol. i, p. 105. Also 

 A. Agassiz, A Visit to the Bermudas in 1894, pi. ii (q.v.). 



2 Student's Lyell, ed. Judd, p. 501. 



