660 REPORT— 1894. 



these opposite results lie side by side. Most of the glaciation is of the negative 

 Mnd, but the areas drained by the Crawcwellt and the Ysi^ethin are covered by 

 glacial cones of dejection. This difference is accounted for in the first instance 

 by the local drainage being opposite to the general drainage, and in the second 

 by the small size of the gathering ground for the ice. From these results it was 

 argued: 1. That drift deposits are, as a rule, left beyond the area of ice-flow. 

 2. That no submergence could possibly have taken place here since the Glacial 

 period, or the features above noted would have been obliterated. 



5. On the Probable Tejnperature of the Glacial Epoch. 

 By Professor T. G. Bonney, D.Sc, LL.D., F.R.S. 



The Alps afford a means of estimating the highest mean annual temperature at 

 which glaciers can begin to form. This must not be more than about 27° F, 

 They also indicate the limits between which glaciers of various moderate sizes 

 form. The author finds that (assuming the present levels of sea and land un- 

 changed) a fall of 20° F. might just bring the Welsh glaciers down to the 

 sea-level, would certainly do it for the Cambrian hills, and would probably 

 produce an ice-shed in the Highlands. A slightly less fall would suffice for the 

 Alps and Pyrenees. Again, a consideration of the traces of glaciers in the 

 Sierra Nevada, Sierra Guadarama, the Apennines, Corsica, Auvergne, the Vosges, 

 and the Schwartz wald shows that these indicate a fall of about 15°, while a 

 greater lowering of temperature would make their glaciers too large. The require- 

 ments of North America, New Zealand, Australia, and Tasmania, and other 

 places would be satisfied by about 15°, and in some cases by less. The limits 

 accordingly of the temperature of theglacial epoch must be from about 12° to 20° 

 lower than at present, according to situation. 



6. On the Inadequacy of the Astronomical Theory of Ice Ages ' 

 and Genial Ages. By Edward P. Culveewell, M.A., F.T.C.D. 



In reference to Sir Robert Ball's numbers, 63 and 37, giving the proportion of 

 summer and winter heat in the northern hemisphere, the numbers on which he 

 bases his theory, it is pointed out that in the latitudes with which the Ice Age is 

 comerned the contrast between summer and winter heat is vastly greater than is 

 shewn by these numbers, which lump together the heat everywhere, at the 

 equator, the poles, and the intermediate latitudes. Nevertheless, though the 

 arguments on which the theory is based may be made much more clear and 

 striking by taking the heat distribution over the northern part of the hemisphere, 

 the method of calling on the imagination to conceive what vast differences of 

 terrestrial temperature may be produced by a slight change in the daily distri- 

 bution of the (unchanged) annual heat is dangerous as not being sufficientlj' based 

 on experience. The argument is that, as the earth is kept at a temperature of, 

 say, 400° F. above zero by sun heat, we might expect a fall of 10 per cent, to 

 lower the temperature by, sa)', 40° F. But in this argument a number of very 

 important elements are overlooked — the diminished radiation from the cooler 

 body, the great time required for any considerable cooling, and the flow of heat 

 by water and air from the hotter to the cooler parts of the terrestrial surface. In 

 fact, so greatly do these causes modify the result that in these islands we now live 

 without inconvenience in a state of deprivation of solar heat during our coldest 

 199 days somewhat greater than that which, continued for the 199 days winter 

 of the great eccentricity period, was believed by Sir Robert to involve necessarily 

 an ice age over the northern hemisphere. 



The estimation of the change in terrestrial temperature due to the changes of 

 eccentricity made in the author's communication is obtained by an entirely 



' A paper giving details of the calculation will be published in the Phil. Mag. 



