﻿260 GLACIAL BEDS OF CAMBRIAN [May I908, 



12. On a FoRMATioK known as ' Glacial Beds of Cambeian Age ' 

 in South Australia. By H. Basedow and J. D. Iliffe. 

 (Communicated by Dr. J. Malcolm Maclaken, F.G.S. Eead 

 November 20tli, 1907.) 



[Abstract.] 



Some 8 miles south of Adelaide a typical exposure of the con- 

 glomerate is bounded on the east by a series of alternating quartzitic 

 and argillaceous bands of rock, comprising the central and western 

 portions of a fan-fold, partly cut off by a fault. Further evidence of 

 stress in this margin is given in the fissility, pseudo-ripple-marks, 

 contortion and fracture, and obliteration of bedding in the quartzite- 

 bands, and in the pinchiug-out of them into lenticles and false 

 pebbles. On the west side the conglomerate is bounded by the 

 ' Tapley's-Hill Clay-Slates,' and there is evidence from the nature 

 of the junction-beds that the conglomerate itself is isoclinally folded. 

 In that portion of the conglomerate which is adjacent to its 

 confines, ' boulders ' of quartzite are apparently disrupted portions 

 of quartzite-bands, since these are in alignment with the truncated 

 portions of bands still existing, and are of similar composition. 

 The Authors are not at present in a position to account for the 

 presence in the conglomerate of boulders of rocks foreign to the 

 beds that border the conglomerate, or of such as possess markings 

 comparable to glacial striae, by their theory of differential earth- 

 movements ; but they consider that a boulder-bed subjected to lateral 

 pressure would probably lend itself to the production of ' false 

 pebbles,' through the disruption of intercalated hard bands within 

 itself or on its boundaries. 



Discussion (on the two foregoing Papers). 



Dr. A. Strahan considered the first paper to be a lucid and con- 

 vincing account of an extremely-interesting series of deposits. The 

 association of schistose rocks and slates with beds of glacial origin 

 had led to the development of some unusual phenomena, but the 

 superinduced structures due to earth-movements on the one hand, 

 and the original characters due to the action of ice on the other 

 hand, appeared to him to have been well illustrated in the two 

 papers. The puckering and the disruption of rock-bands into 

 separate blocks simulating boulders were familiar features in rocks 

 which had been subjected to great pressure. There was this differ- 

 ence, however, between a ' crush-conglomerate ' which had origi- 

 nated in this manner and the beds for which a glacial origin had 

 been claimed, in that the latter contained true boulders of foreign 

 material. The peculiar characters of the glacial deposit had been 

 admirably illustrated in the first paper. Such deposits, whether of 



