lxx PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. lxxix r 



Upper Archaean strata do not form one continuous series ; the 

 occurrence within the system, of several marked unconformities 

 denotes pauses in sedimentation, the uplifting of mountain-chains., 

 the removal of millions of cubic feet of rock, and the subsequent 

 submergence of the denuded land to form the foundation for later 

 accumulations of sedimentary material. It has been calculated 

 that the Pre-Cambrian sedimentary rocks of China (and they are 

 but a part of the whole Archaean System in that region) indicate 

 a lapse of time at least equal to that represented by almost the 

 whole of the Palaeozoic periods. Another computation assigns to 

 the Upper Archaean series a duration possibly equivalent to that 

 represented by all succeeding geological periods combined. It is 

 only with the rocks which can be identified as sedimentary or 

 terrestrial that Ave are concerned, not with those which are igneous 

 in origin, or, if originally sedimentary, too highly metamorphosed 

 to be recognized as such. Our task is to discover traces of 

 Archaean life, to visualize the physical conditions, and to form an 

 estimate of the climate. In the earlier geological periods, we are- 

 assured, the sun may well have been much hotter than it is to-day - 

 but, whether we adhere in the main to the nebular hypothesis, or 

 adopt the planetesimal views of T. C. Chamberlin and H. Gr. 

 Moulton, there would seem to be no reason to suppose that on the 

 Archaean land the temperature was such as cannot be matched in 

 certain regions of the world to-day. Geological researches do not 

 justify the statement that there has been a gradual decline in the 

 temperature at the surface of the earth in the course of ages. 

 There is overwhelming evidence against the old view that the glacial 

 phase in the Pleistocene Period was the result of the ' natural trend 

 of a moribund earth towards a cold senility '. Recurrent glacial 

 conditions were a normal phenomenon throughout geological time. 

 Tillites of Archaean age, reaching 500 feet in thickness, cover a 

 wide area in Canada, occurring at localities 1000 miles apart from 

 east to west and 750 miles apart from south to north. I am 

 indebted to Prof. A. P. Coleman for a photograph of an ice- 

 scratched boulder, reproduced in the recently published book on 

 'Elementary Geology ' by himself & Mr. W. A. Parks in illustra- 

 tion of the glacial origin of these deposits. Archaean boulder- 

 beds are recorded also from South Africa, and tillites, probably of 

 similar age, occur in the Simla district in India. Cambrian, or 

 possibly Upper Archaean, tillites on a large scale have been 

 discovered in China, and undoubted glacial beds in Norway are. 



