1896.] On the Recurrence of Ice Ages. 117 



inclined beds of Opalinthusthone, wherever laid bare, were found 

 to have a perfectly smooth and polished surface 1 . 



If a mass of slipped earth with scratched stones were found 

 resting on a rounded, smoothed, and striated surface and were 

 consolidated into a compact rock it might be difficult in sections of 

 limited extent to feel sure whether we had not before us an 

 ancient consolidated boulder clay — and, if such a mass were by 

 any peculiar combination of circumstances transported piecemeal 

 and the stones scratched by landslips were dropped in clay, so as 

 to appear as isolated boulders, it would be difficult to pronounce 

 very positively as to its origin. 



But the account given of the mode of occurrence of these 

 ancient Australian boulder clays makes it extremely improbable 

 that they can have been produced directly or indirectly by land- 

 slips. In no case do they appear to have been formed on or near 

 the flanks of any steep slopes, but when they rest on a rounded and 

 polished and grooved surface of Archsean or Ordovician rock, 

 the direction of the striae on the solid floor is always from the 

 south, showing that the phenomena are not produced by any 

 merely local agency. 



Some of the boulder clays are interstratified in a vast series of 

 sandstones and conglomerates of marine origin, which attain a 

 thickness in places of 5000 feet. This also points to some remote 

 origin and a mode of transport other than currents of water. 



The marine deposits in which they occur are identified with 

 the Glossopteris and Gangamopteris beds of Tasmania, South 

 Central Africa, India, and Central America. This gives us no data 

 for an exact correlation with any known horizon in Europe. They 

 may have been laid down at any time in the vast interval between 

 the deposit of our newest Carboniferous beds and the first conglo- 

 merates of the Poikilitic series — a period so vast that it may be 

 looked upon as comparable with the time that has elapsed from 

 the age of the New Red to the present day. Those who adopt the 

 very unsatisfactory name Permo-Carboniferous seem to favour this 

 view. There are those however who think that some of them may 

 belong to the same age as part of the Poikilitic or even Jurassic 

 series. It is clear therefore that in the present state of our 

 knowledge the occurrence of glacial deposits in these beds lends 

 us no aid in settling the question of alternate or contemporaneous 

 glaciation of either hemisphere. 



But they do afford very strong evidence in favour of the view 

 that somehow or another the incoming and disappearance of glacial 

 conditions is always connected with great earth movements. 



Here we have a depth of 5000 feet at least getting silted up 



1 " Ueber Bergsturze in den Alpen." Netien Jahrbuch fiir Mineralogie cOc. 1875 

 and footnote. 



