182 NOTES AND EXHIBITS. 



Brit. Mus. Cat., p. 857), and it is a Batrachedra fMacJdstidcdJ. 

 Walker's references of the smaller Micros are entirely hapliazard 

 and consequently not in reality worth, even a passing notice. 



NOTES AND EXHIBITS. 



Note on a Block of Shale from the Hawkesbury Sandstone, by 

 W. J. Stephens, M. A. — I desire to bring before the notice of our 

 geological members, a specimen of shale from a boulder embedded 

 in the Hawkesbury Sandstone at Broughton's Pass, where the 

 tunnel between the Cataract and Nepean Eivers, in connection 

 with the Sydney water supply, is now in progress. The point to 

 which I wish to draw attention at present is that the block has 

 before its deposition among the sands, which have ultimately 

 hardened into rock, been subjected to severe strain and pressure 

 in various directions, producing within its structure those smooth 

 striated surfaces, which are known to miners as '' Slickensides." 

 The unconformity of these slides shows that they were not 

 produced by any uniform or contemporaneous pressures or move- 

 ments, and appear to me to corroborate in a very unexpected way 

 the conclusions at which Mr. Wilkinson has arrived as to the 

 existence of a glacial period during the formation of the Hawkes- 

 bury Eocks, i. e., posterior to the formation of our upper coal, and 

 probably equivalent to the Permian formations of better surveyed 

 countries. Por the irregular and sudden strains which are 

 produced by massive Ice, when drifted by wind or current, forced 

 along the land by pressure, or when slipping and tumbling in huge 

 blocks in consequence of the alteration of their centres of gravity 

 during the process of melting, are precisely such forces as must 

 have produced the phenomena under our notice. Some confirmation 

 may also be found in the absence from the shale thus aifected of 

 any of those fossil ferns which appear so abundantly in similar 

 portions of the formation ; and in the occurrence of thin laminae 

 of fine clay, sometimes with a smooth, mammillated surface, 



