TRANSACTIONS OF SECTION ‘Cc. 795 
produces polygonal figures. These have an even number of sides, and the sides 
are arranged in opposing pairs. This serves to discriminate hexagonal forms due 
to fossil ripple mark from Hitchcock’s supposed fossil tadpole-nests. 
2. The symmetrical, rounded, ripple-mark of the sandy bottom of a stream is 
formed by the alternate acceleration and retardation of current which occurs 
wherever the surface of the water is corrugated by a train of standing waves. 
This form has been called Ripple Drift. The ridges only travel when the whole 
train of water-waves travels; when the train of waves arises from a fived obstacle 
the sand ridges are stationary ; where, however, there is much sedimentation of 
floating sand, the weather slope receives most of the sand shower, and the ridges 
travel upstream. 
3. The Ripple Mark of Dunes is produced when sand grains roli before the 
wind. These ripples are not symmetrical, but they preserve their sectional shape 
during their growth, the height and length increasing in the same proportion. 
They grow laterally in the same way as (1). They are produced by the steadiest 
natural wind, and by a steady artiticial blast even the resistance offered by the 
sand grains being sufficient to produce in yielding air a periodic motion such as 
must be independently produced in water for the formation of the regular ripple 
mark of sea or stream. Flying-sand falling upon the surface of a sand-dune blurs 
the pattern of the ripples; but if the shower be not too thick the grains are soon 
sorted into position as they roll. 
3. Are there Fossil Deserts ? 
By Professor Dr, JoHaNNES WALTHER. 
If we accept the postulate of Lyell, that the phenomena of former periods must 
be explained by the existing phenomena of our earth, we must look around to find 
the regions over which transported material is deposited. It is well known that 
on the bottom of the seas ana lakes the transporting action comes to an end, and that: 
no material is carried out of them. Therefore it is the opinion of most geologists 
that the greater part of our sedimentary rocks were deposited from water. The 
author has spent much time in travelling, for the sake of studying the areas 
occupied by deserts, and finds that, besides the old sea and lake bottoms, there is 
a large area of no drainage in the existing deserts. 
On our globe there is a harmonious system of climatic zones. The largest of 
these is the tropical zone, which forms more than half the surface of the earth. 
The smallest area is the polar regions, which contain only one-eighth of the earth’s 
surface. Between these are intercalated in each hemisphere a temperate zone, 
and a zone of desert, arranged quite symmetrically. By the postulate of Lyell we 
must believe that similar deserts must have existed in the past. The investigation 
of these ancient wastes is a problem not yet worked out. 
4. Notes on the Ancient Rocks of Charnwood Forest. 
By W. W. Warts, ILA., F.GS. 
[Communicated by permission of the Director-General of the Geological Survey.] 
In the course of the re-survey of sheet 155 for the Geological Survey, the 
author was instructed to examine the ancient rocks of Charnwood Forest. The 
boundaries dividing these rocks from the Carboniferous, Triassic, and Plutonic 
rocks had already been mapped by his colleague Mr. Fox Strangways, who had also 
determined with much accuracy the position and general character of all the 
exposures of the older rocks, It was merely left to the author to endeavour to 
get out the succession and structure of these older rocks. 
The ancient rocks of Charnwood Forest appear in isolated spots, sometimes of 
considerable size, through the Trias of the Midland Plain. The oldest rock in 
_ contact with them is the Carboniferous Limestone of Grace Dieu, which is 
dolomitised. Evidence as to their exact age cannot, therefore, be obtained from 
superposition. 
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