1893.] evidence for the Recurrence of Ice Ages. 221 



A ship laden with wheat from San Francisco for Liverpool was 

 caught amongst them. One day 415 were in view from the 

 vessel's maintop. Some of them were 5 or 6 miles in length 

 and between 500 and 700 feet high. This was in the latitude of 

 Holderness and the icebergs were so large that they could not 

 have got near that coast unless there had been a subsidence 

 sufficiently great to submerge the highest mountains in the 

 British Isles if the depression had been uniform over the whole 

 area. Darwin long ago recorded that a fragment of granite was 

 seen on an iceberg between 49° and 50° S. latitude, that is on the 

 latitude of the English Channel. 



Though the sun might shine and the southern breezes might 

 rapidly melt away all that projected above the waves, it would be 

 long before such ice islands finally disappeared. Icebergs that 

 have grounded have been observed to remain for years in the 

 same placed Generally they would be carried by the currents 

 with the wind or against the wind, and where there were no 

 currents would be driven by the wind. It is hard to put a limit 

 on the possibilities of transport of drift and boulders in favourable 

 combinations of ice, coasts, and currents. 



While on the subject of icebergs I would point out in passing 

 how unsafe it is to infer that all grooves and striae even on the 

 solid rock must be due to glacier ice. When we remember the 

 enormous mass of some of those ice islands and the velocity with 

 which they travel, and compare this with what we know of the 

 weight and movement of glacier ice, we may well credit the ice- 

 berg grounding on a boulder-strewn rock with the power of 

 producing grooves and striae. 



Lyell- describes an icefiield seen by Capt. Belcher on the coast 

 of Newfoundland carrying mud and gravel, and explains how, 

 from observations made on the rate of drifting of such masses in 

 those regions, boulders might be transported 1800 miles or so and 

 be dropped as far south as latitude 48°, i.e. the latitude of the 

 northern part of the Bay of Biscay. Hays^ gives examples of 

 icebergs drifted towards equatorial regions as far as 40° N. latitude, 

 that is south of the latitude of Naples, and as far as 36° S. latitude, 

 that is the latitude of North Africa. He ofters abundant testimony 

 as to many of these being laden with drift and boulders. 



If the main mass of this drift is derived from one region we 

 should infer that it was transported to the sea by glacier ice, but 

 if an argument is founded upon a few boulders only of a well- 

 marked rock occurring sporadically here and there in a mass of 

 material derived from other and various sources then we may 



1 Hays, Assoc. Amer. Geologists and Naturalists, Ap. 1843. Howorth, The Glacial 

 Nightmare and the Flood, i. 155. 



2 Presidential Address, Proc. Geol. Soc. 1836, p. 384. 

 ^ O}}. cit. 



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