306 Maiv — Distribution of White Clays and Sands 



could not be removed in watery solution; and if the pockets have 

 been excavated by the chemical dissolution of the limestone, we 

 should expect to find its insoluble constituents left behind in the 

 pockets. 



With the object of ascertaining whether the beds of pure white 

 clay could possibly represent such residue, I procured from Dr. 

 Voelcker the following analysis of the Carboniferous Limestone, 

 forming the walls of the pockets, and of the white clay partly 

 occupying them : 



Analysis of Limestone Wall of Pocket, Nant y Gamer, Llandudno. 



Moisture and combined water 095 i 



Oxide of Iron 0-88 ( Soluble in very dilute 



Alumina 0*15 ( Hydrocbloric Acid. 



Carbonateof Lime in a little Magnesia... 95'53 ' 



Oxide of Iron 085 \ t i v,i • j-i a tt 



.1 • -..n/j i Insoluble m dilute Hy- 



LimT .^.::::::::::::::::::::::::::.:::::::::'.:: o-os drocbioricAcid,form- 



Magnesia and Alkalies (by difference)... 0-28 ^^^| IZZnT 

 Silica 1"62 / 



100-00 



The carbonate of lime and iron would be the constituents re- 

 movable in solution by water charged with carbonic acid, and 

 these we find actually redeposited in the neighbourhood in the shape 

 of ochreous Tufa. The remainder would consist principally of 

 silica and alumina, with traces of the other constituents ; and with 

 such insoluble residue the following analysis of the white clay 

 closely corresponds : 



Analysis of the White Clay from Pockets in Mountain Limestone, 

 Nant y Gamer, Llandudno. 



Moisture and Water of combination 9-96 



Oxide of Iron 1-84 



Alumina 26-43 



Lime 122 



Magnesia 0-82 



Alkalies (by difference) 0-56 



Silica 59-18 



100-00 

 The proportion of silica is somewhat in excess of that contained 

 by the insoluble residue of the limestone ; but as both the clay and 

 the limestone would vary somewhat in their composition, the corre- 

 spondence is as close as could be expected from the result of a single 

 analysis. 



If we suppose this white-clay residue to be gradually thrown off 

 from the sides and bottom of the cavities with the dissolution of the 

 limestone, the sands from the Millstone Grrit deposited from above, 

 and the whole contents gradually lowered as the cavities deepen, 

 we should expect just such a result as the arrangement observed at 

 Nant y Gamer, Holywell Mountain, and the Weaver Hills, viz., a 

 kind of rough stratification broken up, bent and faulted, and here 

 and there inverted. The mass being gradually added to, both from 



