PERCHED BLOCXS AND ASSOCIATED PHENOMENA. 537 



olay, in whicli the majority of the stones are rounded and scratched. 

 The eating back of that drift therefore would not leave such a group 

 as the jSTorber boulders. And they cannot have been blocks carried 

 on glacier ice, as that would imply that they had fallen on to it from 

 higher crags a long way off, whereas in some cases we find that, on 

 the contrary, they came from a rock at a lower level close by. 



In the three cases I have recorded, the positions in which the 

 boulders are found would be out of the line of the principal transport 

 of material. 



In the case of the Cunswick-Tarn boulders there are no high hills 

 to the north. The stones carried on that part of the ice would have 

 got well down into the mass, which would have gravitated towards 

 the east. In the case of Farleton Knot there must have been a 

 time when the ice just split against the end of the hill and was 

 lifted by it, falling away east and west, carrying deep in the body of 

 the ice, below the level of Parleton Knot, the drift it had brought 

 from a distance. 



The situations to which the Pedestal Blocks have been carried 

 shows that the ice must have entirely filled the great valleys of the 

 Kent and its tributaries and the smaller valle}'s opening out into the 

 Craven district, and therefore it must have covered the rock from 

 which the blocks were obviously derived. Now we cannot conceive 

 of any process by which such blocks can have been dug out under 

 the ice and carried forward. In every case where these Pedestal 

 Blocks are found, the parent rock occurs in place close by on the 

 north side — so near that the variation in the snowfall from one 

 season to another would be sufficient to account for the uncovering 

 of the rock from which they were derived, and the picking up and 

 pushing forward of the loosened masses in succeeding seasons of 

 greater advance of the ice to where the Pedestal Blocks now 

 occur. 



Since, then, it is almost impossible that the blocks could have 

 been left by icebergs or be the remains of a Boulder-clay all the 

 rest of which has been washed away by the rain, and since the 

 rare occurrence and limited distribution of such groups of Pedestal 

 Blocks seem to require in explanation some exceptional conditions — 

 not synchronous but similar local conditions in each case- — the 

 following possible explanation, arising out of the observations 

 recorded in the foregoing pages, seems, though not altogether 

 satisfactory, to be the least open to objection with the existing 

 data. 



The great ice-sheet had dwindled away and was still rapidly 

 receding. It pushed along tongues of ice down the principal valleys 

 running south from the Lake-district, from the Pennine Range, and 

 from the Yorkshire Moorlands. Then, as now, or then more than 

 now, there were periods of greater cold and precipitation and periods 

 of milder weather, and in consequence the glaciers sometimes 

 advanced, sometimes fell back, on the whole losing ground. When 

 the glacier had receded a little, then, as now, the Silurian grit of 

 Crummack Dale or the thick- and thin-bedded limestone of Farleton 



