APPENDIX. 



733 



G. 



Bowlders transported by Ice. 



The chapters on superficial detritus were in the press when Mr. Lyell favoured me with the perusal of a most 

 instructive letter from Captain Bayfield, R.N., now employed in surveying the coasts and rivers of our North 

 American colonies, which so strikingly corroborates the views I have attempted to establish concerning the 

 method by which our English bowlders and the associated shells have been deposited, that, with Mr. Lyell's 

 permission, I annex an extract. After a graphic sketch of the geological features of the region, Captain Bayfield 

 thus alludes to the case in question. 



" The bed of the St. Lawrence below Lake St. Peters is full of immense bowlders of primary rocks, most of 

 them (but not all) rolled or water- worn, or with their edges worn off by atmospheric agency, (for I do not 

 believe that all the blocks which appear to be so, have been really water-worn). See pp. 540 et seq. These 

 are principally derived from the Tertiary beds, for they abound in them, even among the shells, and at all levels ; 

 and as the terraces are worn away, the bowlders are left at the foot of the cliffs, and sticking out of sand and 

 clay. Torrents bring them down the steep water-courses at the melting of the snows ; and when they reach the 

 St. Lawrence, the ice moves them every spring. I have seen a granite bowlder, 15 feet in length by 10 in width 

 and depth, transported many yards along a meadow by this agent ; and last spring I watched the lake ice (Lake 

 St. Peter), which takes 2 or 3 days to pass Quebec every spring, and had the pleasure to observe several 

 bowlders of considerable size, and many small stones, sand, earth, reeds and plants on their way down the 

 river, drifting at a rate measurable by the excess of every ebb tide over the preceding flood. The latter flows 

 4f hours, at the rate of 3 knots ; the former about 7-^ hours, at 4 knots. Any bowlders thus transported are 

 liable to be dropped at various points along the bed of the river, as the ice gives way to the increasing tem- 

 perature of the air and water in the spring of the year." 



After showing how freshwater shells, seeds, plants, &c. are similarly transported and tranquilly deposited 

 along with large blocks of stone, amid marine shells, Captain Bayfield gives practical illustrations of the power 

 of the ice of one season in removing large bowlders and deep stakes, which he had caused to be placed in certain 

 positions. These were entirely carried away and replaced by other bowlders, while in the same season a mass 

 of granite, containing 1500 cubic feet, and which he had particularly marked, was transported several hundred 

 yards from its observed position. Again, in speaking of the bowlders which occur in the younger Tertiary de- 

 posits, he says, " They are found in the cliffs at different levels, not resting upon each other, but as if they 

 had been dropped there at widely different times, during a long period, in which a quiet deposition of clay, 

 sand and gravel had been going on, and in which the various genera of testacea had lived and died. Some of 

 the shells are of course broken, and some of the valves are separated, as is the case in the bottom of the present 

 seam; but many have both valves together, although they separate when taken up, because the ligament no longer 

 exists. All idea of these shells (together with the sand, clay and bowlders) having been drifted together into 

 their present positions must be given up at once, when I state the fact, that the Terebratulce psittacece, which 

 you know are so fragile that the smallest stones would be sufficient to destroy them, if carried along with a 

 moderate degree of violence by moving water, are found with their valves together, and their long and brittle 

 teeth entire as when they were living." 



" The whole of the facts, which I have neither time nor space to dwell upon in this letter, lead me to infer 

 that these numerous erratic blocks, from whatever source originally derived, have been dropped from time to 

 time (from ice floes) on the bed of the Tertiary sea." — Extract of a Letter from Captain Bayfield, R.N., to 

 Mr. Lyell, November 1837. 



H. 



Landslips. 



Besides the landslips of Ludlow and Woolhope, one has been partially adverted to, which occurred near 

 Buildwas on the Severn, 12 miles east of Shrewsbury. The reader will find this landslip, " The Birches," 



5 A 



