T. M. Reach — Wind Denudation. 587 



the progress already made in the examination of rocks, with im- 

 proved methods of investigation, it appears probable that a few- 

 more years will suffice for the acquisition of a more complete know- 

 ledge of the numerous varieties of volcanic rocks, of their constituent 

 minerals, and of the various modes in which they may be associated. 



IV. — Wind Denudation. — Eolites. 

 By T. Mellard Eeade, F.G.S. 



I AM not aware that any geological notice has been taken of the 

 effect of the wind on a flat sandy shore, further than the simple 

 removal of the sand therefrom, and its collection on the sea-margin 

 in the shape of sand dunes. 



At the present moment a walk on the shore at Blundellsands has 

 vividly impressed me with the efficacy of this agent — wind — as a 

 denuder. 



Though I have frequently observed the phenomenon I am about 

 to describe, after continued gales from the North- West, I never saw 

 it displayed in so uniform a manner as now. There has been a 

 continuance of wind from the North- West for a lengthened period, and 

 the shore between high-water of neaps and springs is covered with 

 little riclges of sand lying with their axes parallel and in the same 

 direction as the wind. The uniformity and parallelism of direction 

 is most remarkable, and would, supposing they were to be preserved 

 by being filled up with fine silt in places, and ages hence were 

 converted into rock, show to a future geologist unerringly the direc- 

 tion of the wind at the time they were formed. The largest of these 

 little ridges are about 2±in. long, and their height about fin., and as 

 I counted of all sizes 12 in a space of 6 inches, it would be safe 

 to average them at ^ an inch apart. A closer examination shows 

 that the windward or " crag " end, which is the highest, is usually 

 capped with the fragment of a shell, and also that this end is often 

 an overhanging point or veritable " crag." Where best developed, 

 they look like a shower of darts, shot into the ground at the same 

 angle. So much for the facts. Now, what do they tell us ? In the 

 first place, it is quite evident that they are formed by the excavation 

 of the surrounding sand, and indicate the depth to which the sand 

 has been removed ; the shell-capped points are the original surface 

 of the shore, and the shells have acted in preserving an approxi- 

 mately horizontal pillar of earth behind them, like the stones capping 

 the " earth pillars " shown in Lyell's " Principles," have caused the 

 vertical earth pillars by protecting the ground underneath from rain 

 denudation. Here the parallel ceases, for the moisture in one case 

 causes the denudation, whilst the drying up of the moisture by the 

 wind does so in the other. Where these minute ridges are best de- 

 veloped, the shore is always moist, and the wind effects the removal 

 of the sand by drying the surface grains and blowing them away, 

 any little protection in the shape of a larger object, such as a shell 

 fragment protecting the sand in the rear, and so forming a "crag 

 and tail." 



