Glacial theory development history

Further debate, of sorts, took place at subsequent Presidential Addresses by Buckland (1841) and Murchison (1842). In 1842 Murchison, perhaps the most "politically" connected of all the geologists, evaluated all aspects of the theory and came out in favor of the "drift" hypothesis which he had supported in the live GSL debate.

Buckland had already moved towards compromise and accommodation in which he reconsidered the possible action of ice in highland versus lowland settings: "One great cause of the difference of opinion between the diluvialists and the glacialists, is the exclusiveness with which each party would insist upon the agency of the cause which they respectively 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 his theory of expansion as the great locomotive power of glaciers over regions whose surface is too little inclined to admit their progression 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-arranged 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 compromise ; the glacialist will probably abandon his universal covering of ice and snow, and be content with glaciers on the elevated regions 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 [sic] and striated surfaces, in latitudes and at elevations that are no longer within the zones of perpetual congelation." (Buckland 1841 Presidential Address)

Buckland’s and Darwin's subsequent interpretations of Welsh scenery were more or less along the lines of this compromise, with glaciation at higher elevations and glacially-induced floods at lower elevations. This was to be Lyell’s accommodation also, through to the end of his life although he did ultimately accept Alpine glaciation (see Lyell, 1863). Likewise, Darwin never fully abandoned the idea of "drift."

Lyell’s map of 1863: black areas show evidence of glacial action; white evidence of drift; black not submerged during this period.

Late Twentieth Century map of glacial provinces and non-glaciated areas

(NERC: http://www.bgs.ac.uk/science/landUseAndDevelopment/
engineering_geology/formation_engineering.html)

James D. Forbes (1809-1868), a physicist who advanced the study of glacial motion (a highly controversial subject in the 1840s) reviewed all the major arguments that had been advanced to account for the features commonly attributed to either debacles, drift, or glaciers. It is a superb review, not only of the explanations but also of the nature of the debate. He concluded: "To maintain the glacier theory still requires some confidence—some courage. We have not dissembled its difficulties; but by presenting it, as we have endeavoured to view it, with unprejudiced eyes, as fully entitled to rank among geological probabilities, we place it on its most defensible ground, and we venture to predict, at least abroad, a speedy reaction in its favour. Its evidences are such as must be seen, and carefully studied without prejudice, in order to be appreciated; and such evidences, though often required to be sought for, and difficultly found, are not less conclusive when attained. We have constructed a formidable panoply out of the missiles of its adversaries : will they not yield to their own weapons? If they pronounce the theory imperfect, we acknowledge it; but we may very safely challenge them to produce a better or less improbable one, from amongst those already proposed. If they have a new one, we are ready to consider it." (Forbes, 1842)

Buckland, W. 1841 The Geological Society President's Anniversary Address 1841: Geological dynamics – glacial theory. Proceedings of The Geological Society of London v.III (Nov. 1838- Jun. 1842) part II (1841) no.81 p.509-516 http://www.google.com/books?id=giPPAAAAMAAJ&pg=PA509#v

Buckland, W. 1841 On the glacia-diluvial phaenomena in Snowdonia and the adjacent parts of North Wales. Proceedings of the Geological Society of London v. III Part II 1841—1842 no. 84 p.579-584, http://books.google.com/books?id=3qoEAAAAQAAJ&pg=PA579-IA2

Darwin, C. 1842 Notes on the effects produced by the ancient glaciers of Caernarvonshire, and on the Boulders transported by Floating Ice. The Philosophical Magazine and Journal of Science v.XXI July to December 1842 no.CXXXVII (September)p.180-188 http://books.google.com/books?id=flAwAAAAIAAJ&pg=PA180

Mills, W. 1983 Darwin and the Iceberg Theory. Notes and Records of the Royal Society of London, Vol. 38 (1 - August), pp. 109-127

Murchison, R.I. 1842 President's Anniversary Address 1842: The glacial theory. Proceedings of The Geological Society of London v.III (Nov. 1838- Jun. 1842) part II (1842) no.86 p.671-687 http://www.google.com/books?id=giPPAAAAMAAJ&pg=PA671