196 Proceedings of the Royal Physical Society. 



ditions continued unfavourable to the formation of extensive 

 ice-sheets in temperate latitudes, no matter how high the 

 eccentricity of the orbit might have been. The erratics 

 which occur in certain Jurassic and Cretaceous deposits are 

 admitted by most geologists to liave been ice-borne. Now, 

 it is highly improbable that tlie transporting agent could 

 have been coast-ice, for it is hardly possible to conceive of 

 ice forming on the surface of a sea in which flourished an 

 abundant Mesozoic fauna. The erratics, therefore, seem to 

 imply the existence in Mesozoic times of local glaciers, which 

 here and there descended to the sea, as in the north-east of 

 Scotland. The erratics in the Scottish Jurassic are evidently 

 of native origin, and it is most improbable that those which 

 have been met with in the chalk of England and France 

 could have floated from any very great distance. How, then, 

 can we explain the appearance of local glaciers in these 

 latitudes during Mesozoic times ? The geographical con- 

 ditions of the period could not have favoured the formation 

 of perennial snow and ice in our area, unless our lands were 

 at that time much more elevated than now. And this is the 

 usual explanation. It is supposed that mountains much 

 higher than any we now possess probably existed in such 

 regions as the Scottish Highlands. It is easy to imagine the 

 former existence of such mountains. So long a time has 

 elapsed since the Jurassic period, that the Archaean and 

 Palaeozoic areas cannot but have suffered prodigious denuda- 

 tion in the interval. But, when one considers how very 

 lofty, indeed, those mountains must have been, in order to 

 reach the snow-line of Jurassic times, one may be excused 

 for expressing a doubt as to whether the suggested explana- 

 tion is reasonable. At all events, the phenomena are, to say 

 the least, as readily explicable on the supposition that the 

 snow-line was temporarily lowered by cosmical causes. 

 Even with eccentricity at a high value, no great ice-sheets, 

 indeed, could have existed, but local snow-fields and glaciers 

 might have appeared in such mountain-regions as were of 

 sufficient height. And this might have happened without 

 producing any great difference in the temperature of the sea, 

 or any marked modification in the distribution of life. In 



