TRANSACTIONS OF SKCTION C. 



721 



least linve been carried forward involved in the matrix, ond f^liiciatod chiefly by ilM 

 partii'lt"'- Under the microscope the jmrticles exhibit most of the varieties of iorm 

 and ^'laL-intion tiint lire found amonf? hirj^er bouMers. Tiie gtructuro of tlie till 

 in maiiv o]ien sifiiations siiows that the axes of it.s atones have been turned l»y a 

 I'omiiiiin force in tlie direction of ^'hu-ialion; exliibilin<,'a rough arranf,'ement cnui- 

 iMiraliie to tlio tluxion-htrueture of iirneous roeliH, the smaller bouhlers dividing' 

 arniiiid and apparently driftin;,' past tiie larfj;er, like the tide round an anchored 

 Nkiir. This structure, whicli has lieen found by the author over many luuidrcds 

 (if square miles, chiefly in tlu; North of iMiirland, indicates that at least a surface- 

 IiiviT i)f tlie till was dra;r>red alony, with a shearing movement of particle upon 

 liiiiticlf. ])ro(lueini.' intimate frlaciation within its mass. Proofs are adduced that 

 this iiiming layer was in p'Ueral a surface-layer oidy, and that the till did not, as 

 has eftcii bf'eii suj)]tose(l, move forward en viossr, licliiu','' up its additions from 

 Irncatb. This appears to be the only intelli;;ihle explanation of the order (as 

 well as the structure) of the boulder-clays of which the auth(3r has any jiractical 

 kiiowli'ijii-e. In up-lyini.' situations, where the drift consists of raw material, 

 tliixiiiii-structures are seldom to be detected. In sheltered spots they are not pene- 

 lailv 'Itvclojied. 'I'hey are characteristic of well-kneaded till in open s-ituations, 

 lialile, however, to obsemvuion by contortions within the mass. Of twelve ex])eri- 

 ini'iital atti'inpts made near the watershed of J'lngland in I'iast (^imberlandjOOU '.((Ml 

 I'let abiive the sea, to determine tin; ice-movenieut from this structure alone, (•if,''hi 

 were correct, three indeterminate, and only one misleading. Tiie luessuve and 

 miiVfiiH'iit capable (d" producinfr tliis widi's])read Huxion-struclure seem to have 

 liwii tliat of some mass vast and far-spreading — closely investing, sIow-iJi(;viiig, 

 and heavily (iragging — such as glacier-ice. It needs only to be as-sunit'd tiuit the 

 ((inlliient glaciers coromunicated something of their own movement and structure 

 til the ground-raoraino below. 



o. Oil the (11 arid On'iji'ii of Lalce Tidsi'ns. 

 ll>j Ai.i-UKD R. C. Sklwv.x, LL.R, F.L'.S. 



As we are all aware, a great deal has been said and wi'itten on the manner in 

 which the numerous rock basins now hohling lakes have been foi'uu'd, and that 

 tlii'y liave heen assigned by Uaiusay and many other geologists to the scooping 

 power of ice. 



In 1870, Ramsay, Hull, .Tames Geikie, .ludd, Fisher, IJonney, and Hugh 

 Miller took part in tlu» discussion of this ciuestion.' 



On December '20, 187(5, following the very interesting remarks on this subject 

 liy the authors above named, I wrote as follows : '' 



' In readinii^ the correspondence and remarks on the origin of Lake basins, in the 

 Xnveinber and other numbers of the '(teological Magazine,' it has occurred to nu^ 

 that the glacial origin of these basins may be explained without supposing the ice 

 to have scooped them out of solid rocks, such as we now se(> around them. 1 have 

 heen led to this idea by a study of the phenomena connected with the decomposi- 

 tion of rocks ill Kitii in southern latitudes - Australia and Brazil. 



'Similar facts, I am informed, may likewise be seen in .South Carolina, 

 (ieorgia, &c. 



' In these southern regions, which have never been glaciated, the surface over 

 niore or less extensive areas consists of quite soft decomposed rock, and mining 

 operations have shown that tlu! decomposition has been, from some unexplained 

 cause, very irregular in its action, and that often great masses resembling boulders 

 lire quite unchanged though completely surrounded by the decomposed material ; 

 and the varying depth to which the decomposition has extended has resulted in 

 producing an underlying solid rock surface, as full of hollows and depressions of all 

 shapes and sizes as can be found in any of our northern lake regions. And if wo 

 admit that prior to the Glacial period these northern lake regions were similarly 



188i. 



' Gnnlo/fical Magazine, vols. iii. and iv., 187C an I 1877. 

 * Geological Magazine, vol. iv., p. 93, 



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