1 -1 8 Geological Society : — 



and a depression of tho land for at least 200 feet. The overlying 

 shelly boulder-clay shows that the ice-sheet returned and overflowed 

 Lewis, scooping out the older drift-beds and commingling them with 

 its bottom moraine. The absence of kames was commented upon, 

 and shown to bo inexplicable on the assumption that such deposits are 

 of marine origin, whilst if they be of torrential origin their absence 

 is only what might be expected from the physical features of the 

 islands. The only traces of Postglacial submergence are met with 

 at merely a few feet above present high-water mark. 



2. " Cataclysmic Theories of Geological Climate." By James 

 Croll, Esq., LLJD., P.R.S. Communicated by Prof. Ramsay, LL.D., 

 F.RS., P.G.S. 



The author commenced by calling attention to the great diversity 

 of the hypotheses which have been brought forward for the explana- 

 tion of those changes in the climate of the same regions of the earth's 

 surface which are revealed by geological investigations- — such as alte- 

 rations of the relative distribution of sea and land, of the ecliptic, 

 and of the position of the earth's axis of rotation — all of which, he 

 maintained, have proved insufficient or untenable. Sir William 

 Thomson has lately maintained that an increase in the amount of 

 heat conveyed by ocean-currents, combined with the effects of clouds, 

 winds, and aqueous vapour, is sufficient to account for the former 

 prevalence of temperate climates in the Arctic regions ; and this view, 

 the author stated, he had himself been contending for for more than 

 twelve years. He thinks, however, that alterations in the eccen- 

 tricity of the earth's orbit is the primary motive cause, whilst Sir 

 William Thomson believes this to be the submergence of circum- 

 polar lands, which, however, in Miocene times, appear to have been 

 more extensive than at present. He pointed out that a preponderance 

 of equatorial land, as assumed by Sir Charles Lyell to account for 

 the milder climate of Arctic regions in Miocene times, would rather 

 tend to loss of heat by rapid radiation into space, whilst water is re- 

 markably powerful as a transporter of heat; so that, in this case, 

 equatorial water rather than equatorial land is needed. 



In speaking of the glacial climate, the author maintained that 

 local causes are insufficient to explain so extensive a phenomenon. 

 He indicated that we are only too prone to seek for great or cata- 

 clysmic causes ; and although this tendency has disappeared from many 

 fields of geological research, this is not the case in all. His explana- 

 tion of the causes of a mild climate in high northern latitudes is as 

 follows : — Great eccentricity of the earth's orbit, winter in perihelion, 

 the blowing of the south-east trades across the equator perhaps as far 

 as the tropic of Cancer, and impulsion of all the great equatorial 

 currents into northern latitudes ; on the other hand, when, with 

 great eccentricity, the winter is in aphelion, the whole condition of 

 things is reversed : the north-east trades blow over into the southern 

 hemisphere, carrying with them the great equatorial currents, and 

 glacial conditions prevail in the northern hemisphere. Thus those 

 warm and cold periods which have prevailed during past geological 



