PROCEEDINGS OF SECTION C. 45^ 



grooving and striation of rock surfaces in southern Australasia, in 

 Permo-Carboniferous time, appears to be proved by the following 

 facts : — 



1. The persistence of striae and grooves over great distances, ana 

 their systematic radiation from near some common centre or gathering 

 ground. 



2. In the Bacchus Marsh area, as Messrs. G. Sweet aiid C. C. 

 Brittlebank and the author have shown, the grooves made by the ice 

 are developed both on the stoss-seite and lee-seite of old valleys with 

 steep sides. Floating ice could not possibly have accomplished such 

 work as this. 



3. The nature of the ground mass of the till varies with that of 

 the subjacent rock, proving that the till, as regards its ground mass at 

 all events, was manufactured locally. This could not have been 

 accomplished by any form of ice other than that of glaciers or ice sheets. 



4. There appears to be an absence for the most part of microscopic 

 or macroscopic marine fossils in the till beds proper. Such fossils as are 

 found are plants, usually in a more or less fragmentary condition. 



5. In the next place, on the assumption that the glaciation was 

 the work of land ice, there is evidence in the great thickness of the glacial 

 beds, with their interstratified deposits, that the first Permo-Carboni- 

 ferous glacial epoch, that of the Lower Marine series, lasted for a con- 

 siderable amount of time. In the Bacchus Marsh district, for example, 

 as already pointed out by Messrs. C. C. Brittlebank, G. Sweet, and the 

 author, the glacial series attains a total thickness of over 2,000ft. In 

 South Australia, in the Inman Valley, the section supplied by the 

 Back Creek bores for coal, and the natural sections afforded by the 

 hills and valleys, show that the glacial series there is over 1,000ft. 

 certainly in thickness.* As recent observations by the author on the 

 Wynyard beds of Tasmania show, this same glacial stage of the Lower 

 Marine series, as developed there, has a thickness of about 1,200ft. 



If now we compare these thicknesses with those of the glacial 

 beds left by the great Pleistocene ice sheets of the Northern Hemisphere 

 we find that where they attained their maximum thickness, towards 

 their margins, they are about 150ft. thick. It is estimated that even 

 this comparatively small thickness of strata required for its formation 

 some scores of thousands of years. If, therefore, so great a period of 

 time was needed during the Pleistocene epoch, in order to form 150ft. 

 of glacial and interglacial strata, what period of time was needed, 

 during the Permo-Carboniferous period, in order to produce a thick- 

 ness of no less than 2,000ft. of similar beds ? 



Next, the evidence in the type districts of Wynyard for the land 

 glaciation, and of Lochinvar for the evidence of floating ice, both show 

 that an important interglacial epoch or age intervened between the 

 Lower Marine glacial stage and that of the Upper Marine. Evidence 

 for this interglacial stage is afforded by the intercalation of the Greta 

 coal measures, over 100ft. in thickness, and containing in places fully 

 40ft. of coal between the Upper and Lower Marine series. 



* Mr. Howchin now estimates their thickness at about 1,500ft. 



