318 A. P. Coleman — Paleohotany and the 



One important example of ancient banded rocks of this 

 kind has received little attention and may be referred to 

 specially here. The middle member of the Sudbury 

 Series, called the McKim Graywacke, consists of thin lay- 

 ers of interbanded gra^^vacke and slate, i. e., of coarser 

 and finer particles, usually from half an inch to two or 

 three inches in thickness. The banding has not been con- 

 nected with glacial materials. As the beds are 4,000 feet 

 thick, they indicate alternating conditions of deposit last- 

 ing thousands of years ; and no theory of formation which 

 does not include seasonal times of flood and slack water of 

 great regularity is admissible. 



These very ancient banded rocks of Canada have a 

 parallel in the banded Bothnian rocks of Finland as 

 described by Sederholm, who believes them to have been 

 formed, if not in a glacial period, at least in a cold climate. 



It is evident that the testimony of the world's banded 

 slates of different ages, reaching back almost to the ear- 

 liest times, must be taken seriously into account in all 

 speculations as to the beginnings of geology. 



Ice Ages. 



The most impressive of all the proofs of severe ancient 

 climates incompatible with any theory of an earth con- 

 tinuously cooling down until the Pleistocene to to be found 

 in the ice ages of the far past. Wliatever theory one ad- 

 vocates as to the cause of ice ages, it is evident that the 

 presence of great ice sheets on low ground in several con- 

 tinents at once during Permo-Carboniferous times cannot 

 be reconciled with a mild and equable climkte due to the 

 unexhausted internal heat of the earth. The presence of 

 great ice sheets in Australia, South Africa, South Amer- 

 ica and India, as admitted by Knowlton himself, is fatal 

 to the theory he advocates, and no suggestion that the 

 period of cold was short affects the conclusion. While 

 these continents were heavily glaciated, in places close to 

 sea-level, as shown by associated marine beds. North 

 America was frost-touched near Boston and in the Yukon 

 region, and both France and Germany have glacial depos- 

 its that seem to be of the same age ; so that all the conti- 

 nents were affected. Siissmilch and David's proof of 

 three repetitions of ice invasion in New South Wales, 

 with long intervals between them, demonstrates that gla- 

 cial conditions were very long continued, though broken 

 by interglacial intervals of moderate temperatures. 



