62 PEOCEEDINGS OP THE GEOLOGICAL SOCIETY. 



the New Eed at Leamington, and from the Wealden at Mark 



Cross. 



Sand with Quartz chemically deposited on the surface of the grains. 



Many authors have already described what they have called 

 crystallized sand ; but I think they have often mistaken its true 

 nature. In some cases, if not in all, the grains are not quartz 

 simply deposited in a crystalline form, but are sand of perfectly 

 normal character, on. the outer surface of which a greater or less 

 amount of quartz has been deposited in crystalline continuity with 

 that of the original nuclei. The phenomena are like what hap- 

 pens when an irregular fragment of a soluble crystal is placed in 

 a concentrated solution of the same salt slowly evaporating. The 

 first stage of the process is the restoration of the broken angles ; 

 and then deposition goes on over the whole exposed surface, in 

 perfect optical and crystalline continuity, so as to change a broken 

 fragment into a definite crystal. We observe precisely the same 

 facts in the case of the sands now under consideration. 



Grood examples of the early stage of the process are seen in the 

 Old Eed of Cockburnspath. The original grains are composed of 

 quartz containing cavities and granules, whereas that deposited on 

 the surface is quite clear, and the line of junction often perfectly 

 distinct. Deposition, to any marked extent, has taken place only 

 over a few ; and in almost every case merely the pyramidal ends 

 of the crystals have been reproduced, as shown by fig. 1. 



Pig. 1. — Sand-grain with slight Pig. 2. — Sand-grain with much 

 deposition of Quartz. Quartz deposited on the surface. 



The more complete development of a crystalline form, by depo- 

 sition over the whole surface, is well seen in the sand of the 

 Vosges, described by M. Daubree, to whom I am indebted for a 

 specimen. The nuclei of original waterworn sand are composed 

 of quartz containing many cavities and granules ; the outer surface 

 is rough and discoloured ; and over the whole very limpid quartz 

 has been deposited ; so that the contrast is very marked. None 

 has been deposited on the surface of the felspar grains ; and when 

 a grain is composed partly of quartz and partly of felspar, the de- 

 posit has taken place only on the quartz, as in the case shown by 



