S22 Geological Society. 



of this kind that have come under my observation, the surfaces have 

 only been cut off transversely and ground smooth, like the shores 

 of the present seas ; but they have no such parallel striae as those 

 which are of general occurrence beneath diluvium or drift*; nor 

 have large erratic blocks from distant regions been found mixed with 

 the gravel of any of the older conglomerate rocks. 



One great cause of the difference of opinion between the dilu- 

 vialists and the glacialists, is the exclusiveness with which each 

 partj' would insist upon the agency of the cause wliich they respect- 

 ively adopt : the diluvialist apparently errs in refusing to admit the 

 agency of glaciers in mountain valleys that are below the existing 

 limits of ice and snow ; whilst Agassiz may have erred in urging too 

 far bis theory of expansion as the great locomotive power of glaciers 

 over regions whose surface is too little inclined to admit their pro- 

 gression by the force of gravity ; a middle way between these two 

 extreme opinions will probably be found in the hypothesis, that large 

 portions of the northern hemisphere which now enjoy a temperate 

 climate have at no very distant time been so much colder than they 

 are at present, that the mountains of Scotland, Cumberland, and 

 North Wales, with great part of Scandinavia and North America, 

 were within the limits of perpetual snow accompanied by glaciers ; 

 and that the melting of this ice and snow was accompanied by 

 great debacles and inundations which drifted the glaciers with their 

 load of detritus into warmer regions, where this load was deposited 

 and re-ai'ranged by currents at vast distances from the rocks in 

 which it had its origin. The contest will probably be settled, as in 

 most cases of extreme opinions and exclusive theories, by a com- 

 promise ; the glacialist will probably abandon his universal covering 

 of ice and snow, and be content with glaciei-s on the elevated re- 

 gions of more southern latitudes than now allow of their formation ; 

 the diluvialist, retaining his floating icebergs as the most efficient 

 agents in the transport of drift and erratic blocks to regions distant 

 from their place of origin, may also allow to glaciers their due 

 share in the formation of morains and striated surfaces, in latitudes 

 and at elevations that are no longer within the zones of perpetual 

 congelation. 



PHOTOGRAPHY. 



A valuable application has been made by Captain Ibbetson of 

 a Photogenic process for rapidly producing perfect drawings of 

 fossil shells on metallic plates, from which, when fixt by the en- 

 graver's tool, lithographic transfers may be rapidly multiplied to an 

 almost indefinite extent. This process promises to be applicable to 

 organic remains of every kind, and consequently of great utility 

 in Palaeontology. From a beautiful fossil starfish I sent by one day's 

 mail to Captain Ibbetson, in London, I received, by the next mail, 



* They are sometimes also perforated by lithodomous molhiscs, and other- 

 wise beset with parasites, which indicate a period of tranquillity between the 

 action of the forces by which they were shorn away or made smooth, and 

 the deposition of the stratum that was subsequently formed over them. 



