On the occurrence of Enhydros. 33 



At the spot marked 1 (on the outlier) the stones were first 

 met witli. It was the widening of a vein bearing about 

 N. 30 E. and dipping to the north, forming an irregular 

 cavity about 2 feet wide by 3 feet long, the small vein still 

 continuing. 



This nest was filled with scales of chalcedony and fine 

 clay, interspersed with the enhydros generally in groups, 

 their planes being in contact with the planes of others, 

 forming what appeared a solid lump ; it required, however, 

 but very little force to separate them into distinct perfect 

 stones. There were sometimes 10 or 15 thus joined. 



Some parts of the cavity were tilled with scales and clay 

 'only, the scales being nearly in the same direction, the 

 edges looking like those of pieces of mica with frayed edges. 



The appearance of the scales might be accounted for by 

 supposing the cavity to be filled with a solution of silica, 

 holding in suspension fine clay. The rough walls would be 

 first coated with coarse chalcedony, then — from an excess of 

 clay — a fine film of it might have been deposited, then a thin 

 coat of silica, forming a scale and so alternating until the 

 cavity became filled. 



Another place in which the enhydros occur (marked 2 in. 

 plate) is in soft fine grained granite. The vein is about 

 I inch thick, expanding to a few inches in one place. This 

 one is very regular in its strike (W 5° S) and dips to the N. 

 The stones found here were unusually large, some as much 

 as 5 inches across, but very dark in colour and nearly all ■ 

 broken ; not more than one in ten is perfect in either vein, 

 the large ones are almost invariably imperfect. 



There seem to have been three distinct movements of the 

 rocks. During the first and probably most violent one the 

 fissures in the silurianand hard granite were filled with quartz. 

 During the next movement the chalcedony was deposited as 

 solid veins from | to 1 inch thick, in the hard granite, and 

 as scales ; and enhydros later in the silurian and soft granite. 

 The last movement dislocated these veins, g-nd accounts for so 

 many broken waterstones. This seems to have been the 

 course of events, as the quartz veins are cut through by the 

 chalcedony ones, and these again in places show signs of 

 displacement. 



The enhydros consist of chalcedony with a hardness 

 equal to topaz ; they are many-sided and irregular in form, 

 bounded by true planes. Their colour varies from dark 

 brownish yellow and nearly opaque to quite colourless and 



D 



