[The following appeared in the Geological Magazine for July, 
1893, p. 323-] 
The Cause of Crateriform Sand 
Dunes and Chms. 
BY WILLIAM SHONE, F.G.S. 
T St. Anne’s-on-the-Sea, Lancashire, there are a great 
number of very large sand-hills. ‘They are for the most 
part crateriformed in the centre, from the gyratory movement 
of the wind in stormy weather There must be some cause, 
however, which determines the course of the wind, for its 
natural action, one would suppose, should be to carry away 
Dunes by sweeping them before it. 
I believe the znz/cal cause of crateriform sand Dunes is rain. 
The Dunes are so porous that the rain does not run off the 
outsides, but sinks through them, carrying particles of sand with 
it as it sinks to lower levels. This is especially the case when 
the base of the sand-hill rests upon quicksand. The internal 
abstraction of sand is greatest in the centre and least at the 
sides, hence the formation of a cen/ral initial cup. 
During the wet season in September and October, 1892, I 
had many opportunities of studying such phenomena at St. 
Anne’s-on-the-Sea. In one instance I was fortunate enough to 
observe one of these rain-made hollows formed. It occupied 
the centre of a deep crateriform sand Dune. It was forty-eight 
inches in diameter, and twenty inches deep in the middle. The 
centre of the hollow had reached the quicksand which underlies 
the base of the sand-hill. 
Cwms. 
May not the similar action of rain, during a lengthened period 
of time, account for the origin of Cwms. For instance, the 
beautiful Cwm which forms the N.W. front of Cader Idris, in 
the hollow of which lies Llyn-y-Gader. Through the moraine 
matter which stretches across the Cwm, I have heard, beneath 
the surface, the noise of the surplus water of Llyn-y-Gader 
rushing away. Rain is, I think, the Cwm maker, as well as the 
crateriformed Dune maker, and both are the effects of subaérial 
denudation and subterranean erosion acting in unison. 
A SEQUEL. 
On October the sth, 1893, I received a letter from PROFESSOR 
G. A. Lenour, M.A.; F.G.S., in which he stated as follows :— 
“J have only just had the opportunity of reading your very 
interesting note in the Gevlogical Magazine, on Cwms formed 
