The estimates made by geologists, which will appeal more directly to the geological student, also vary considerably, though they bear some proportion to those which have been put forward by the physicists. Prof. S. Haughton[128] assigned a period of 200,000,000 years for the accumulation of the rocks of the geological column; Mr Clifton Ward[129] one of 62,000,000 years, after studying the rocks of the English Lake District, and allowing for the gaps in the succession; Mr A. R. Wallace[130] further lowers the time for the formation of the column to 28,000,000 years; Sir A. Geikie[131] gives 73,000,000 years as the minimum and 680,000,000 as the maximum; while Mr J. G. Goodchild has lately[132] estimated the period at over 700,000,000 years. [Footnote 128: _Nature_, vol. XVIII. p. 268.] [Footnote 129: Ward, J. C., 'The Physical History of the English Lake District,' _Geol. Mag._ Dec 2, vol. VI. p. 110.] [Footnote 130: Wallace, A. R., _Island Life_, Chap. X.] [Footnote 131: Geikie, Sir A., 'Presidential Address to the British Association,' _Report Brit. Assoc._, 1892.] [Footnote 132: Goodchild, J. G., _Proc. Roy. Soc. Edinburgh_, vol. XIII. p. 259.] Interesting as these figures are, they probably convey little to the ordinary reader, and it is doubtful whether the geologist is really affected by them to any extent when picturing to himself the vast duration of geological time. One numerical estimate probably does impress him, namely that made by Croll as to the date of the Great Ice Age, for if the Ice Age be so remote as Croll imagined, the commencement of earth-history must be inconceivably more remote; as Croll's estimate is not generally accepted, it is doubtful how far geologists are thus influenced, and probably the fact which does impress them most, leaving fossils out of account, is the very little change which has occurred in historic or even in prehistoric times as compared with the vast changes which are familiar to them after studying the strata of the geological column.