1865.] 



WALLACE — FLOS FERRI. 



415 



semitransparent, and beautiful*, the occurrence of the branched arra- 

 gonite is very rare. I have not heard of more than four or five caverns 

 in which it has been found, except in small pieces. In the Nent- 

 head mines stalactites are never found except near the surface, or 

 in the old works. 



Two of these caverns have come under my notice. One of them 

 in a north vein of the Silver Band Mine, where the Great Limestone 

 forms its walls. The vein is not strong. On the north side of a 

 short portion the limestone was flatted for a few feet from the vein. 

 The flats contained lead-ore and other minerals, all of them much 

 decomposed. Nearly all the sulphide of lead was changed into car- 

 bonate, and the round lumps of carbonate, mingled with the oxides 

 of iron, had not unfrequently crumbled into small particles, having 

 the appearance of fine sand of a light-brown colour. Only a few 

 fathoms west from where the arragonite was found, the vein and fiat 

 are filled chiefly with impure barytes not much affected by the de- 

 composing agents. The cross section (fig. 1) wiU enable me to de- 

 scribe more clearly the phenomena connected with the cavern. 



Fig. 1. — Section of a Cavern in the Silver Band Mine. 



1. I .3. Great Limestone. 



That part of the cavern marked a Avas filled wdth rubbish and 

 pieces of sandstone ; without doubt the latter had fallen through the 

 * The transparent stalactites exhibit double refraction. 



2 F 2 



