J. Hopldnson — Structure of Oraptolites. 353 



the Pennine range of hills? The progressively upward action of 

 ground-ice during storms may partly furnish an answer to this 

 question, but I think the main explanation must be sought for in the 

 denuding action of sea-waves encroaching on the top of the hill, 

 which at one time may have been higher than at present. A pre- 

 viously-existing conical eminence ma,y have been truncated by the 

 sea, so as to leave the " plain of marine denudation," or table-land, 

 now forming the summit of Wasdale Hill ; and it is possible, if not 

 probable, that the hill may have lost several hundred feet of its 

 height during the process of natural quarrying which supplied the 

 floating ice with all the boulders which found their way across Stain- 

 more Pass. The preponderance of Wasdale Hill granite among the 

 larger transported boulders (at least in many areas) may be ac- 

 counted for by the fact that the compactness and distance between 

 the joints or fractures of the granite would cause it to break up into 

 blocks much larger than those resulting from the dilapidation of the 

 neighbouring rocks, many of which indeed, would break up into 

 mere chips or splinters. 



Concluding Remarhs. — The foregoing facts and considerations lead 

 us to the conclusion that the cause which dispersed the boulders from 

 Wasdale Hill radiated from the hill as from a centre. But the in- 

 significant summit of the hill could not have supported a nearly 

 sufficient quantity of land-ice to have furnished the floating ice 

 on its breaking-up, while land-ice in such a position could not have 

 detached the blocks from the solid rock. The blocks therefore must 

 have been detached and rounded by sea-waves and sea-ice, and 

 floated and transported by the latter. Winds may have partly or 

 chiefly propelled the ice which floated the boulders found in the 

 neighbourhood of Wasdale Hill, but currents must chiefly have 

 carried the ice with the boulders which are found at great distances. 

 Though the finer part of the pinel and loam must in a great measure 

 have been derived from a source different from that which supplied 

 the granite boulders, the accumulation of the pinel and loam and 

 imbedding of the boulders must have taken place contemporaneously 

 while the land was submerged. 



The causes of the glaciation and mode of accumulation of the 

 Drifts of other parts of the Lake District will form the subject of a 

 future article. 



n. — On the Steuctuee and- Affinitijss of the G-enus 



DiCRANOGBAPTUS. 



By John Hopkinson, F.G.S.^ F.E.M.S. 



(PLATE XVI.) 



THE name Dieranoffraptus was proposed by Hall, in his Memoir 

 on the " Graptolites of the Quebec Group " (p. 112), for 

 certain forms of Graptolites, some of which were then included in 

 the genus Bidymograpsus, and others in Biplograpsus. He, however, 

 only considered these forms as constituting a sub -generic group of 

 his genus Climacograptus, believing them to have a similar structure. 



