D. Mackintosh— Section near Mold, Flintshire. 67 



VI. — On a New Section op Pre-Gla.cial White Clay and Sand 



NEAR Mold. 

 By D. Mackintosh, F.G.S. 



MR. GEORGE MAW, in tke Geological Magazine, Vol. IV. 

 pp. 24 and 299, has described a number of sections in Flint- 

 sbire and Denbighshire in which white clay or sand occurs under 

 Boulder-clay. A newly-exposed section near Colomendey Hall, 

 about three miles from Mold, is very important on account of the 

 complete series of glacial drifts by which the white clay is overlain. 

 I lately examined it in company with Mr. Manning, of the Chester 

 Natural Science Society. 



Section of Deposits near Colomendey Hall. 

 (order descending). 



1. Brown clay, with a few nearly angular stones, some of them scratched; 7 feet in 



thickness. 



2. Sandy and clayey gravel, with numerous stones (both small and rather large), most 



of them rounded, and some of them scratched ; from 2 to 3 feet. 



3. Brown clay, with many stones, and at its base large boulders, most of them much 



scratched and striated ; about 6 feet. 



4. Bluish or dark-coloured clay, with many stones, the latter much polished, and 



intensely and often uniformly scratched and striated ; greatest thickness about 

 6 feet.i 



5. The stony blue clay graduating downwards into laminated stoneless blue clay, with 



black carbonaceous matter ; about 3 feet. 



6. The above passing downwards into more or less laminated white clay graduating 



into vphite sand ; about 1 8 feet. 



7. Broken and decomposing chert. 



8. Carboniferous Limestone rock. 



Bemarhs. — The basin in which the above deposits are packed is 

 said to be about 300 yards in diameter. The broken chert, white sand, 

 and clay would appear to have been accumulated before the glacial 

 period. Before or at the commencement of the deposition of the 

 blue clay there would seem to have been a sweeping of carbonaceous 

 matter into the hollow, and a washing up, staining, and partial 

 re-deposition of the upper part of the white clay. Severe glacial 

 conditions must have accompanied the accumulation of the blue 

 clay ; and during the continuance of these conditions, a more or less 

 different source of supply must have furnished the materials com- 

 posing the lower brown clay. The gravel-bed and the clay above 

 would appear to have been deposited during very mitigated glacial 

 conditions. The white clay, according to Mr. George Maw, may be 

 regarded as the residue of the limestone, after the calcareous matter 

 was carried away by aqueous dissolution. If so, the silica and 

 alumina composing the white clay, however short a distance it may 

 possibly have travelled in this instance, must in one case at least 

 have been carried a considerable distance from the parent limestone 

 rock. In the Mold valley, three miles off (as lately ascertained by 

 boring operations), the order of the drifts and white clay is much 

 the same as at Colomendey, though the underlying rock belongs to 



^ Nearly all that can be seen of the blue clay fills up a hollow in the white clay. 

 But a bore-hole at some distance from the pit reveals its existence in the same 

 position relatively to the other deposits. 



