448 SCIENTIFIC RECORD FOR 1883. 



the Great Pyramid of Gizeh, gigantic mountains, sueli as the Hima- 

 layas, and great elevated plateaus and table-lauds do not affect the 

 pendulum-indications in any sensible manner, except in certain cases 

 where upon elevated continents there appears to be a veritable defect 

 of attraction instead of the excess which might be expected. Indeed, 

 the observations are sufficiently striking to seem to point to the sup- 

 position that not only under every great mountain, but even under 

 the whole of every large continent, there are enormous cavities. More 

 than this, the attractions at the surface of all the great oceans appear too 

 great to agree with the distribution presumed by Clairant's formula, 

 which is exact enough for most purposes. Sir G. Airy's suggestion 

 that the base of the Himalaya range reaches down into the denser liquid 

 interior, and there displaces a certain amount of liquid, so that the ex- 

 terior attraction is thereby lessened, is one which, inherently improba- 

 ble, fails to have any application in explaining why the attraction above 

 the seas should be greater than over the continents. M. Faye pro- 

 pounds the following solution of the difficulty : Under the oceans the 

 globe cools more rapidly and to a greater depth than beneath the surface of 

 the continents. At a depth of 4,000 meters the ocean will still have a 

 temperature not remote from 0° C, while at a similar depth beneath 

 the earth's crust the temperature would be not far from 150° C. (allow- 

 ing 33 meters in depth down for an increase of one degree in the inter- 

 nal temperature). If the earth had but one uniform rate of cooling all 

 over it, it would be reasonable to assume that the solidified crust would 

 have the same thickness and the same average density all over it. It is 

 therefore argued that below the primitive oceans the earth's crust as- 

 sumed a definite solid thickness before the continents, and that in con- 

 tracting, these thicker portions exercised a pressure upon the fluid 

 nucleus tending to elevate still further the continents. This hypothesis, 

 M. Faye thinks, will moreover explain the unequal distribution of land 

 ' and sea around the two poles ; the general rise and fall of continents 

 being determined by the excess of density of the crust below the oceans, 

 and by the lines or points of least resistance to internal pressure being 

 at the middle of continents or at the margin of the oceans. {Nature, 

 XXII, p. 200.) 



Professor Geikie has made an interesting contribution to the precise 

 measurement of the rate at which the exposed surfaces of different kinds 

 of rock are removed in the processes of weathering. The important in- 

 fluence of the atmosphere in geological problems needs elucidation from 

 all sides, and it occurred to him that data of at least a provisional value 

 might be obtained from an examination of tombstones freely exposed to 

 the air in graveyards in cases where their dates remained still legible 

 or might be otherwise ascertained. He accordingly paid attention to 

 the older burial grounds in Edinburgh, and has gathered together some 

 facts which have sufficient interest and novelty to render it desirable 



