328 G. H. Kinahan — Erroneous Names of Drift. 



undermined and brought down ; but a terrace can be formed only 

 within the vertical limits just named. Hence it is clearly im- 

 possible for a river to shape rock into a terrace that is inclined 

 several degrees from the horizontal. 



Thus far then the objection against the fluvial origin of these rock 

 ledges are : 1st, Many of them are situated a thousand feet above 

 where any stream that could give rise to them could possibly flow. 

 2nd, The scars on both sides of the valleys often maintain a rude 

 parallelism for long distances ; a convex outline on the one side being 

 opposed to one correspondingly concave on the other, even where the 

 distance across the valley between the two scars exceeds a mile. 

 Lastly, each bed gives rise to a form of terrace that has some more 

 or less marked peculiarity which appears at whatever inclination that 

 particular bed may be lying at, and at whatever elevation it may 

 occur above the bottom of the valley. 



{To be concluded in our next Number.) 



VIII. — The Erroneous Nomenclature op the Drift. 

 By G. H. Kinahan, M.E.I.A. 

 rpHE necessity for a reform in the present nomenclature of the Drift 

 JL is apparent from the different papers on the subject, but more 

 especially from the note appended to Mr. Bird's supplementary 

 paper on the "Post-Pliocene Formations of the Isle of Man" 

 (Geol. Mag. May, 1875, p. 228). The author of this paper states 

 that this glacial drift is " generally marine." May I ask how a 

 drift deposited in the sea can be called glacial ? Undoubtedly, 

 originally, it was ice-formed, but so also are all the drifts or the 

 major portion of them, that at the present day are accumulating in 

 the seas round our islands, in our lakes, and in our river valleys ; 

 let them be shingle, gravel, sand, silt, or a boulder drift. A normal 

 glacial drift must be deposited direct from ice. If, however, 

 subsequently it is sorted and re-arranged by water or any other 

 agent, it ceases to be glacial. If any other definition of glacial drift 

 is allowed, in glacial drift may be included shingle, gravel, sand, 

 silt, besides the different boulder-clays, at the caprice of the 

 explorer or writer, if he can only prove that subsequent to their 

 being in their present condition, they had been normal glacial drift. 

 At the present day, if the sea, the waters of a lake, a river, or even 

 rain, is denuding glacial drift, a boulder-clay may be forming, 

 identical in aspect, with these so-called " stratified glacial drifts " ; 

 they evidently are not glacial drifts, yet they are formed by similar 

 secondary arrangements to those drifts that some observers would 

 rank as glacial. 



In all hilly ground (such as the Isle of Man), after the ice had 

 retired and the sea occupied its place, the margin of the latter, 

 rivers, etc., formed cliffs in the glacial drift, at the base of which, 

 sands and such-like deposits accumulated ; the latter, in many cases, 

 were subsequently covered up by the weathering from the cliffs, the 

 newer depositions being stratified boulder-clays, but of meteoric 

 origin, and probably formed long after all the ice had left the 



