48 THE GLACIAL PERIOD IN AUSTRALIA, 



to form a spui' there particularly, but also at other places, one 

 may expect to find these traces. The ice-stream moving down the 

 valley presses with the greatest force against the j^rotruding parts 

 of the sides of the valleys on the way, against the spurs. Any 

 rocks or small stones which may have been accidentally frozen 

 into the ice, and which may be situated near the bottom, will, 

 when hard and protruding, cut deep grooves in the rocks which 

 they pass over slowly, with the immense pressure of the whole 

 glacier behind them. In this way the protruding rocks will be 

 polished down more and more. As soon as the glacier retreats 

 these polished rocks will be left bare and exposed to the air. 



In our case these rocks are granite without exception, and their 

 surface withers very fast. The grooves and scratches soon become 

 oblitered, but the shape of the extensive polished surface remains 

 and indicates to an experienced eye immediately the action of 

 moving ice. 



Further proofs for the correctness of the supposition that we 

 have to do with the effects of ice, are furnished by the relative 

 position of joints and surface. The polishing goes on of course 

 quite regardless of joints, and consequently in 99 cases out of a 

 hundred, one will find the polished surface cutting the joints at 

 varying angles, and not parallel to the direction of any one system 

 of joints. 



I have examined the direction, dip, &c., of joints in 12 of the 

 rocks which I consider as glacier polished, and found in every case 

 that the direction of the polished surface followed the direction of 

 the valley, the direction in which the glacier there, once had moved, 

 and was never parallel with any system of joints. The rounded, 

 always convex shape, and particularly also one fact proves the 

 glacial origin of these surfaces without a doubt — viz., that the 

 polished surface is continuous for a long distance in some places. 

 That is to say, in those parts numerous isolated rocks, in different 

 parts of the hill side or spur, are polished down to exactly the 

 same level. 



One of these instances, on a spur high above a tributary to the 

 Snowy River, was so remarkable, that my assistant, who had never 



