ANNIVERSARY ADDRESS OF THE PRESIDENT. IxXXvii 



appear difficult to find much reason, the various metals, such as 

 silicium, aluminium, calcium and the rest, became oxides from coming 

 in contact with oxygen. We have sufficient oxygen in our atmo- 

 sphere, supporting the animal and vegetable life which now exists, 

 and which probably also during a long lapse of geological time has 

 existed on the earth's surface, to permit the assumption that in an 

 early state of our globe oxygen may readily have been far more 

 abmidant among the gaseous portion of the matter forming our 

 planet, including its atmosphere, than at present, when animal and 

 vegetable life is adjusted to the quantity remaining. 



As far as we are acquainted with the substances forming our globe, 

 we may have an oxidized solid crust, supporting in parts a compara- 

 tively thin and irregularly-disposed covering of saline water, and 

 enveloped by a gaseous covering, the interior not composed of oxides, 

 but more or less homogeneous, allomng for the effects of any heat 

 which may be supposed to remain in it, and for the densities due to 

 the gravitation towards its centre of all the particles of matter of 

 which the earth is composed. 



When we have to consider any changes in the earth's axis of 

 rotation due to the absence of homogeneity in its component parts, 

 we have also to regard the probability of this want of homogeneity 

 extending to a depth at which it would have' any appreciable value. 

 As far as the distribution on the face of the earth of the igneous rocks 

 is known to us, — rocks whence, with the exception chiefly of lime- 

 stone deposits (many of which have been accumulated by means of 

 animal life), so many others have been formed, — we do not find any 

 accumulation of masses of very different density in one part more 

 than another, so as to have produced very marked differences in 

 density on at least the surface of our spheroid. On the contrary, 

 we find the probable distribution of granite and granitic rocks with 

 the same density, very uniform in various parts of the earth's surface, 

 and their abrasion has furnished abundant materials for other rocks. 

 The like happens with the heavier compounds of hornblendic and 

 felspathic substances, and the strata derived from them. Masses of 

 limestone are indeed here and there more irregularly distributed, 

 but as the limestones do not much differ from the granites in specific 

 gravity, no great effects would follow their unequal distribution, more 

 particularly when we take into consideration the small depth to which 

 they would probably descend in the earth's crust. 



We have also to regard the effects arising from the dislocation of 

 the strata, as noticed by Sir John Lubbock. There are few geolo- 

 gists who are not now prepared to admit that the surface of the 

 earth, since we may assume any solidity in that surface, has been in 

 an unquiet state, some large areas moving upwards, some downwards, 

 and these movements sometimes repeated in the same area : deposits 

 crushed and folded against each other here and there in long lines, 

 so that parts of them are thrust high up above the level of the sea, 

 while masses of accumulations are forced asunder in other situations, 

 and mineral matter raised from beneath occupies parts of the area 

 over which thoy previously spread. Up to the present time mineral 



