PREVENTING SMOOTHNESS OF GROUND. 225 



pieces. If so, we must then ask if they were quite ana- 

 logous. The rising would not be expected to be seen, as 

 I saw the place in July, and with us the ground is much 

 levelled by rain soon after the thaw. In a grass-field in 

 the Carse of Gowrie I noticed irregular forms of the size 

 of those made on a gravelly walk close to it. 



But if the causes are similar here and in Iceland, why is 

 the result different ? In Iceland the frost lasts longer and 

 the hardness will be much deeper. The expansion will there- 

 fore be from a much further point of pressure, and will 

 affect a greater surface at a time ; deeper, heavier masses 

 also will be contracting on cooling, and greater forms will 

 take place. I think this a fair mode of reasoning. 



Now we must endeavour to identify these flat forms on 

 the gravel with the raised forms on the grass-field. The 

 identity sets itself off very strikingly in aspect, similarity 

 of size and form occurring in the same climate. This is a 

 long way towards the matter already. We require now 

 to widen the cracks and raise the forms. If grass grew 

 on the flat forms, it would raise them by the upward pres- 

 sure, but it would not grow in the crack, which the rising 

 would widen. The crack would then become a deposit for 

 water or a drain, and the grass would more and more seek 

 the upper part until a natural limit was attained. What 

 is the natural limit? As soon as the crack became so 

 wide as to allow light and other requirements of a plant, 

 and was so wide as to be able to take off the water rapidly 

 by the extent of its surface, it would assert the rights of 

 that surface, and grow grass- crops also. 



This seems fair reasoning. But a difficulty occurs. 

 The first figure, I foot wide, had a crack at the side about 

 half an inch wide. The figure when raised is still I foot 

 wide, and the space taking the place of the crack is equally 

 wide. I do not see how they adjusted themselves; but it 

 may be that in such cases the original figure was 2 feet 



SER. III. vol. v. Q 



