CXXX11 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



glacier is considered to be composed of solid ice, his observations 

 tended to show that all the phenomena are analogous to what might 

 be expected in a moving semifluid or pasty liquid like lava, and hence 

 that a glacier ought to be considered ice in this imperfect state of 

 condensation. However difficult it has been to ordinary observers to 

 convince themselves that the ice they saw before them with its lofty 

 pinnacles and its huge crevices, and which they could split with an 

 axe into angular fragments, was a semifluid substance, the theory of 

 Forbes has yet for several years been received as a satisfactory ex- 

 planation of the phenomena ; but Professor Tyndall has now satis- 

 factorily proved that the structure of ice (a structure which had 

 been previously ably illustrated by M. Schlagintweit) is such that 

 it can be readily crushed into its constituent particles, and again by 

 pressure reconsolidated, so as to conform to all the variations of form 

 of the mould through which it is forced. The comparison of the 

 results of direct experiment at the laboratory of the Eoyal Insti- 

 tution with the actual phenomena of the glaciers themselves has 

 convinced Professor Tyndall, and I may fairly say every one who 

 has listened to or read his lectures upon the subject, that his expla- 

 nation of the mode in which ice is enabled to pass through all the 

 accidents of movement, and to change its form without losing its 

 continuity, is as satisfactory as it is philosophical ; but it must be 

 evident to all, that the theory of Professor Tyndall explains all 

 the phenomena of glacier-motion, but not the cause of that motion. 

 Professor Forbes had this latter point in view when propounding his 

 theory of semifluidity ; and we must now look to Professor Tyndall, 

 who stands, from his zeal, intelligence, and high mental training, 

 in the foremost rank of Alpine observers, to clear up the only diffi- 

 culty now remaining.*' 



Descriptive Geology. — The great zeal with which palaeontological 

 research has been pursued, and the vast accession to the numbers of 

 extinct animals and plants, have necessarily required the cooperation 

 of the most able naturalists with the geological explorer, in order to 

 ensure a correct determination of the epochs of the earth's history by 

 the peculiarities of their respective faunae and florae. The geologist 



* On this point I think it right to refer to the paper of my respected friend 

 the Rev. Canon Moseley, F.R S., on the motion of glaciers, published in the 

 ' Proceedings of the Royal Society/ and in which he adopts the facts of Forbes 

 and Tyndall as being satisfactorily established. He considers the motion due to the 

 successive expansions and contractions of the ice according to the variations in 

 its temperature, just as in any other solid, and independent of the congelation 

 of water which may have filtered into its cavities. This theory he illustrates by 

 a curious fact, observed first in a scientific manner by himself, at the Cathedral 

 of Bristol. The sheets of lead with which a portion of the building had been 

 covered are observed to descend gradually down the inclined plane of the roof, 

 even tearing out the nails by which they have been fastened to the rafters, and 

 that solely by their successive expansion and contraction. This substitution of 

 the simple principle of the contraction and expansion of the ice as a solid body, 

 each tending to promote its descent on an inclined plane, for the hypothetical one 

 of the expansion by congelation of water filtrating into either the crevices or cracks, 

 is unquestionably very ingenious, although some of our able philosophers have 

 considered it insufficient to account for phenomena exhibited on so large a scale. 

 Mr. Moseley, however, is about to reply to the objections of Professor Forbes and 

 others in a second paper on the subject. 



