218 



cutting wind on a tenacious surface. The marks are preserved by a 

 very thin coating of fine earth, and the opposite surface is not a 

 counter-impression, but has pecuHarities of its own. After the in- 

 tervention of a few other seams, there follow repetitions of those 

 ah-eady described, but somewhat varied. In conclusion, an expla- 

 nation of all the appeai-ances is attempted. The author suggests 

 that they have been caused by showers of sand, driven by a strong 

 wind upon the surface of the rocks before they had become har- 

 dened. The sand, he supposes, has been derived from volcanoes in 

 activity at the period, and the existence of which is inferred by the 

 igneous character of many of the neighbouring hills. 



2. On the Causes of Local Peculiarities of Temperature in 

 diffei'ent parts of Great Britain. By James Elliot. Com- 

 municated by David Milne, Esq. 



Many remarkable diversities of temperature are observed in this 

 island, which have not yet been satisfactorily accounted for, either 

 by difference of latitude or of elevation, by shelter or exposure, or 

 by the influence of currents in the ocean. It is attempted to shew 

 that other causes usually assigned have no validity, — that the prox- 

 imity of high, and consequently cold mountains, has no effect in 

 cooling the low ground near them, even when their summits are 

 covered with perpetual snow, and that a difference in the clearness 

 of the sky, or in the radiating power of the surface of the ground, 

 produces no effect on the average temperature. The great cause, 

 then, of the diversities in question is to be found, the writer con- 

 siders, in the latent heat of vapour, — in the caloric disengaged 

 by its condensation, or absorbed in its formation. He shews the 

 great addition which may be made to the temperature of the atmo- 

 sphere by a heavy fall of snow to the windward, and, on the other 

 hand, the great loss of temperature by evaporation. The differences, 

 in the amount of rain, he attributes almost entirely to the general 

 slope of the surface over which the wind passes, in connexion with 

 the height of the ground over which it has previously passed, and 

 the differences of evaporation to the material of the soil and its cover- 

 ing, and to its state of drainage, natural or artificial. Some experi- 

 ments are then detailed, shewing the amount of moisture capable of 

 being retained by various coverings of soil, moss, &c., and the ex- 

 tent to which some of these promote evaporation. The writer con- 



