ON SOME PERCHED, BLOCKS AND ASSOCIATED PHENOMENA. 527 



43. On some Perched Blocks and associated Phenomena. By 

 Thomas M^Kenny Hughes, M.A., F.G.S., Woodwardian Pro- 

 fessor of Geology, Cambridge. (Eead June 23, 1886.) 



It is important to record any facts which may throw light on the 

 conditions which prevailed immediately after the age of extreme 

 cold which is commonly spoken of as the Glacial Period. 



In the north of England round the Lake Mountains we have many 

 opportunities of examining details where the physical geography is 

 so marked that we may often feel considerable confidence in the 

 interpretation we put upon some of the facts observed. But even 

 there we meet with curious phenomena upon the exact explanation 

 of which we cannot yet with safety insist. Among these is the 

 manner of occurrence of certain perched blocks. 



Perched blocks we will define to be masses of rock placed in more 

 or less elevated positions at which they could not have arrived by 

 any of the ordinary operations of nature now in action in that 

 locality. We wish by this to exclude all " tumblers " or masses which 

 have fallen from the cliffs above, such as the " Bowder Stone," in 

 Borrodale, and also rocks trundled along by the mountain-torrents, 

 which often in storm are swollen to the size of great rivers and leave 

 small deltas of loose material or isolated blocks in positions we should 

 never believe them capable of reaching as we watch the silvery 

 trickling thread of water in fair weather. 



Some perched blocks may have been dropped off the margin of 

 glacier-ice; some may have been floated on coast-ice or bergs. 

 Among the perched blocks there are some, too, which all would 

 allow had been transported to their present locality by the former 

 action of the ice, though they may have dropped into the exact 

 position they now occupy in much later times, owing to the washing 

 away of the finer part of a great mass of Boulder-clay in which 

 they were imbedded. The removal of this, by postglacial denuda- 

 tion, has left them stranded where they are now found. 



But there is yet another class of blocks, the mode of occurrence of 

 which requires some exceptional explanation. 



These are what we may call the pedestal boulders, that is, blocks 

 perched on pedestals of limestone. The first question is, how were 

 the pedestals formed ? and the second, how did the boulders get 

 there ? It is on the phenomena connected with these that I propose 

 to offer a few observations. 



I will take three groups which have the chief points in common 

 but differ in some important circumstances : — 



i. The boulders near Cunswick Tarn, West of Kendal. 



ii. The boulders on Parleton Knot (the grey-limestone hill which 

 forms such a conspicuous feature on the east of the railway, about 

 haKway between Carnforth and Kendal). 



iii. The boulders on Norber Brow, north of Austwick, in the 

 Craven District. 



AU these rest upon striated rock ; all belong to a rock which 



