540 



THE ICEFLOE HYPOTHESIS EXAMINED. 



of land and sea may have been such, as to have permitted the production of icebergs, 

 which, being dislodged from the shores of Cumberland, might have been drifted into the 

 straits of the sea then existing to the south of Bridgnorth. 



If, however, we admit that icefloes or icebergs may have been the true method of 

 transport, it is right to allude to an objection which has been raised, that the blocks in 

 Shropshire (as in many other parts of the world) are generally so much rounded and 

 worn, that they rather convey the impression of having been rolled under water, than 

 of having been simply removed from their parent rocks in vessels of ice. Now, 

 although this objection cannot be altogether obviated by replying, that modern atmo- 

 spheric agency may have worn away their angles and scored their surfaces, (for we 

 sometimes witness the same appearances when the bowlders are dug out from great 

 depths beneath gravel, clay and sand) still the attrition of their surface may be well 

 explained under any one of the following conditions. 1st. They may have been carried 

 down by streams to the shores, and have been long bowldered there, previous to their 

 insertion in the ice. 2ndly. They may have been fragments, which, falling from 

 the adjacent rocks, were exposed to the action of water on the shores before their 

 transport by ice. 3rdly. It is well worthy of remark, that granite is so prone to 

 desquamation 1 , that nearly all granitic chains are topped with rounded masses, which, 

 though really in situ, have often the appearance of being bowlders ; and these, if 

 dislodged from cliffs and imbedded in icefloes, would at once present the appearance 

 objected to, though they had never been rolled under water. Finally, it may be ob- 

 served, that if transportation in ice be supposed, we can account rationally for the 

 blocks occupying for the most part the surface or upper portions of the drift, for we 

 know from modern analogies, cited by Captain Bayfield, that icefloes, in narrow bays 

 or straits, are generally stranded on coasts or shallow shores. 



Such were the arguments I employed to show how far the ice theory would account 

 for the dispersion of erratic blocks over the central parts of England 8 . Others had 

 put forth this theory in respect to fluviatile, lacustrine, and subaerial phenomena, and 

 I applied it to the ancient condition of the region in question, when it was permanently 

 beneath the sea. But still, in common with other geologists, I was unprepared with 

 adequate data to show how such phenomena could have occurred in our latitudes during 

 the period before the present, while geological evidence went rather to prove the preva- 

 lence of a former higher temperature 3 . No one, in short, had then the means of ac- 



1 See Macculloch on the Tors of Cornwall, Geol. Trans., Old Series, vol. ii. p. 66. 



2 The memoir containing these views was read before the Geological Society, in 1835, and was subsequently 

 commented upon in Mr. Lyell's Anniversary address, Feb. 1836. (Proceedings of the Geological Society.) 



3 The erratic blocks on the surface of the earth are so much larger than any fragments found within the 

 ancient strata, that some geologists have termed the epoch of their production " the block period," ("Periods 

 Clysmien" of Brongniart). It is quite manifest that as far as our present evidences teach us, the period n which 

 these blocks were transported differed essentially from any which preceded it, and the difference can only be well 

 accounted for by a prodigious change of climate. Geologists, therefore, naturally connect the absence of these 



