450 Notices of Memoirs — Professor Sollas's Address 



Not merely the earth's crust, but the whole of earth-knowledge is 

 the subject of our research. To know all that can be known about 

 our planet, this, and nothing less than this, is its aim and scope. 

 From the morphological side geology inquires not only into the 

 existing form and structure of the earth, but also into the series of 

 successive morphological states through which it has passed in 

 a long and changeful development. Our science inquires also into 

 the distribution of the earth in time and space ; on the physiological 

 side it studies the movements and activities of our planet ; and not 

 content with all this, it extends its researches into setiology and 

 endeavours to arrive at a science of causation. In these pursuits 

 geology calls all the other sciences to her aid. In our common- 

 wealth there are no outlanders ; if an eminent physicist enter our 

 territory we do not begin at once to prepare for war, because 

 the very fact of his undertaking a geological inquiry of itself 

 confers upon him all the duties and privileges of citizenship. 

 A physicist studying geology is by definition a geologist. Our 

 only regret is, not that physicists occasionally invade our borders, 

 but that they do not visit us oftener and make closer acquaintance 

 with us. 



Early Sistory of the Earth : First Critical Period. 



If I am bold enough to assert that cosmogony is no longer alien 

 to geology, I may proceed further, and taking advantage of my 

 temerity pass on to speak of things once not permitted to us. 

 I propose therefore to offer some short account of the early stages 

 in the history of the earth. Into its nebular origin we need not 

 inquire — that is a subject for astronomers. We are content to 

 accept the infant earth from their hands as a molten globe ready 

 made, its birth from a gaseous nebula duly certified. If we ask, as 

 a matter of curiosity, what was the origin of the nebula, I fear even 

 astronomers cannot tell us. There is an hypothesis which refers it 

 to the clashing of meteorites, but in- the form in which this is 

 usually presented it does not help us much. Such meteorites as 

 have been observed to penetrate our atmosphere and to fall on to the 

 surface of the earth prove on examination to have had an eventful 

 history of their own, of which not the least important chapter was 

 a passage through a molten state ; they would thus appear to be the 

 products rather than the progenitors of a nebula. 



We commence our history, then, with a rapidly rotating molten 

 planet, not impossibly already solidified about the centre, and 

 surrounded by an atmosphere of great depth, the larger part of 

 which was contributed by the water of our present oceans, then 

 existing in a state of gas. This atmosphere, which exerted a pres- 

 sure of something like 5,0001b. to the square inch, must have 

 played a very important part in the evolution of our planet. The 

 molten exterior absorbed it to an extent which depended on the 

 pressure, and which may some day be learnt from experiment. 

 Under the influence of the rapid rotation of the earth the atmosphere 

 would be much deeper in equatorial than polar regions, so that in 

 the latter the loss of heat by radiation would be in excess. This 



