312 James Croll — On the Glacial Ei^och. 



Dec. 1856. — Four large icebergs, one of them 700 feet high, and another 500 feet, 



were met with in lat. 50° 14' S., long. 42° 54' E. 

 Dec. 25th, 1861.— The " Queen of Nations " fell in with an iceberg in lat. 53" 45' S., 



long. 170° 0' W., 720 feet high. 

 Dec. 1856.— Captain P. Wakem, ship "Ellen Eadford," found in lat. 52° 31' S., 



long. 43° 43' W., two large icebergs, one at least 800 feet high. 



Mr. Towson states that one of our most celebrated and talented naval surveyors 



informed him that he had seen icebergs in the southern regions 800 feet high. 

 Mar. 23rd, 1855. — The " Agneta" passed an iceberg in lat. 53° 14' S., long. 14° 41' E., 



960 feet in height. 

 Aug. 16th, 1840. — The Dutch ship "General Baron von Geen " passed an iceberg 



1000 feet high in lat. 37° 32' S., long. 14° 10' E. 

 May_15th, 1859.— The "Eoseworth" found in lat. 53° 40' S., long. 123° 17' W., an 



iceberg as large as "Tristan d'Acunha." 



In the regions where most of these icebergs were met with the 

 mean density of the sea is about 1*0256. The density of ice is "92. 

 The density of icebergs to that of the sea is therefore as 1 to 1-115 ; 

 consequently every foot of ice above water indicates 8-7 feet below 

 water. It therefore follows that those icebergs 400 feet high had 

 3480 feet under water, — 3880 feet would consequently be the total 

 thickness of the ice. The icebergs which were 500 feet high 

 would be 4850 feet thick, those 600 feet high would have a total 

 thickness of 5820, and those 700 feet high would be no less than 

 6790 feet thick, which is more than a mile and a quarter. The 

 iceberg 960 feet high sighted by the "Agneta" would be actually 

 9312 feet thick, which is upwards of a mile and three-quarters. 



Although the mass of an iceberg below water compared to that 

 above may be taken to be about 8-7 to 1, yet it would not be always 

 safe to conclude that the thickness of the ice below water bears the 

 same proportion to its height above. If the berg, for example, be 

 much broader at its base than at its top, the thickness of the ice 

 below water would bear a less proportion to the height above water 

 than as 8*7 to 1. But a berg such as that recorded by Capt. Clark, 

 500 feet high and three miles long, must have had only -Jy of its 

 total thickness above water. The same remark applies also to the 

 one seen by Capt. Smithers, which was 580 feet high, and so large 

 that it was taken for an island. This berg must have been 5628 

 feet in thickness. The enormous berg which came in collision with 

 the "Eoyal Standard" must have been 5820 feet thick. It is not 

 stated what length the icebergs 730, 960, and 1000 feet high re- 

 spectively were ; but supposing that we make considerable allowance 

 for the possibility that the proportionate thickness of ice below 

 water to that above may have been less than as 8-7 to 1, still we can 

 hardly avoid the conclusion that the icebergs were considerably 

 above a mile in thickness. But if there are icebergs above a mile in 

 thickness, then there must be land-ice somewhere on the southern 

 hemisphere of that thickness. In short, the great Antarctic ice-cap 

 must in some places be over a mile in thickness at its edge. 



Few things have tended more to mislead geologists in the interpre- 

 tation of glacial phenomena than inadequate conceptions regarding 

 the magnitude of continental ice. Without the conception of con- 

 tinental ice the known facts connected with glaciation would be 



