190 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



and crushed into a narrower width. The shortening of the earth 

 crust thus effected has been estimated in the case of the Rocky 

 Mountains at 29 miles, of the Himalayas at 62, the Alps at 76, and 

 the Appalachians at the large figure of 200 miles. 



Then there is the periodicity of mountain growth. The great 

 epochs of mountain-building, such as the Caledonian, to which the 

 chief Scottish and Welsh mountains are due, the Hercynian, re- 

 sponsible for the Pennine and South Wales, and the Alpine which 

 gave us "the wooded, dim, blue goodness of the Weald", were asso- 

 ciated with vast continental development; and each was separated 

 from the next by a period of relative inactivity lasting dozens of 

 millions of years. 



Further, there is the fact that the vigor of mountain-building, 

 of volcanoes, and of other manifestations of unrest, has shown no 

 sign of senility or lack of energy. The geologically recent Alpine- 

 Himalayan range is as great, as lofty, and as complicated in struc- 

 ture, as were any of its precursors. The active volcanoes of Kilauea, 

 Krakatao, or St. Pierre, and those recently extinct in Northern 

 Ireland and the Scottish Isles, were as violent and efficient as any of 

 those of the Paleozoic Era. The earth is "a lady of a certain age", 

 but she has contrived to preserve her youth and energy as well as 

 her beauty. 



But it was when Lord Kelvin's dictum struck from geology its 

 grandest conception, time, that it became vital to re-examine the 

 position. He had demonstrated that, if the earth had been con- 

 tinuously cooling down at its present rate, its surface must have been 

 too hot for the existence of life upon it a limited number of million 

 years ago. The concept of geological time, indicated by Hutton 

 in his famous saying that in this enquiry "we find no vestige of a 

 beginning — no prospect of an end", had been confirmed by data 

 accumulated through the painstaking researches of a host of com- 

 petent and devoted observers all over the world. To them, familiar 

 with the tremendous changes, organic and inorganic, that the 

 earth had passed through since Cambrian time, it was wholly im- 

 possible to compress the life story of the earth, or the history of 

 life upon it, into a paltry 20 or 30 million years. The slow gi'owth 

 and slow decay of mountain range after mountain range, each built 

 out of, and in some cases upon, the ruins of its predecessor; the 

 chain of slowly evolving organisms, vast in numbers and infinite in 

 variety; told plainly of long eons of time. And the duration of 

 these eons can be dimly realized when it is recalled that, within 

 a small fraction of the latest of them, man, with the most primitive 

 of implements and the most rudimentary culture, has succeeded 

 in penetrating to the uttermost corners of the world, and developed 

 his innumerable languages and civilizations. 



