Earth's Early History. 317 



form and steady supply of heat from the earth's interior 

 under the assumed screen of clouds. Another type of 

 evidence, the regular banding of clays with finer and 

 coarser layers, the ''annual rings'' of the rocks, he leaves 

 as doubtful. In this, I believe, no physical geologist will 

 agree with him. The banding of Pleistocene clays, counted 

 by De Geer up to 12,000 annual layers in Sweden, was un- 

 doubtedly due to seasonal changes, summer and winter; 

 and there are many instances of precisely similar banding 

 in older rocks, sometimes associated with undoubted 

 glacial deposits, but sometimes unconnected with known 

 tillites. An excellent summing up of the evidence for 

 seasonal banding of slates of various ages is given by 

 Sayles, whose attention was directed to the subject by the 

 occurrence of well banded slates with the Squantum tillite 

 of Carboniferous age.^ Where sought for, such banded 

 rocks are usually found with the tillite of an ice age, ex- 

 actly as the Pleistocene banded clays are connected with 

 the bowlder clay of the latest glacial time. Siissmilch and 

 David describe great thicknesses of them in connection 

 with the wonderful Australian glacial and interglacial de- 

 posits of late Carboniferous and early Permian times. 

 At Seaham, New South Wales, for instance, such banded 

 beds are held to indicate 3,000 years of deposit in a glacial 

 lake. Their figures and descriptions leave no doubt as to 

 the origin of the shales, since they are entirely similar to 

 the banded clays {varve clays) of the Pleistocene.^ Sim- 

 ilar banded slates, sometimes enclosing ice-rafted bowl- 

 ders, are found with the Cobalt tillite, of Huronian age ; 

 and no doubt other examples of the sort will be found 

 when geologists have their attention directed to the sub- 

 ject in glacial deposits of other ages and in other parts of 

 the world. 



It may be looked on as proved, then, that the year had 

 warm and cold seasons in the late Carboniferous and 

 Permo-Carbonif erous ; and also in the Huronian glacial 

 times. 



If this is true of the regularly banded sediments oc- 

 curring with tillites, there is reason to believe that similar 

 banded sediments no tknown to beassociated with bowlder 

 clay, had a corresponding origin. Sayles would even 

 make the banding evidence of glaciation. 



^ E. W. Sayles, Seasonal Deposition in Aqueo-glacial Sediments, Mem. 

 Mus. Comp. Zool., Harvard, vol. 43, No. 1, 1919. 



^ Proc. Roy. Soc, New South Wales, 53, 270, 1919-20. 



