842 [B.N.F.O. 



(2). The Zeolitic and Calcitic Layer, deposited im- 

 mediately on the surface of the hullite, consists of a 

 thin layer, occasionally of fibrous zeolites, but gener- 

 ally composed of calcite. The usual thickness of 

 this layer is about one-sixteenth to one-eighth of an 

 inch, and it is mostly much weathered. The 

 zeolitic parts of this layer appear to> consist chiefly 

 of natrolite, and occasionally this passes into 

 analcime. Small crystals of chabazite are also to 

 be found in this portion of the vein. The zeolites 

 and calcite are rarely found together, but when they 

 occur thus, the former have been deposited upon 

 the latter. The thin layer of calcite frequently 

 develops sporadic crystals of that mineral j4 to* %' 

 of an inch in length. 



{3). The Chalcedonic Layer, coating the second layer, 

 and sometimes entirely filling the central portion of 

 the vein. After a single layer of chalcedony had 

 been deposited, the large sporadic crystals of calcite 

 again appeared here and there on its surface. 

 These crystals in turn became enveloped by a 

 second, and by succeeding layers of the chalcedony, 

 and the finest examples of spherical crystalline 

 growth may be found in the latter. In such in- 

 '.tances, there is often in the chalcedony immediately 

 investing the calcite crystals, a zone of white, 

 opaque, jaspery material, containing calcareous and 

 zeolitic matter. 



The Carnmoney chalcedony exhibits all the typical 

 structures of that mineral. In colour it varies from bluish- 

 white to bluish-grey, the latter being more translucent than the 

 whiter varieties. A beautiful translucent specimen, with typical 

 reniform structure, was found to> have a specific gravity of 

 2.582. A section through the reniform chalcedony shows very 

 well its fibrous and spherically-crystalline arrangement. The 

 chalcedony is almost entirely composed of these 'radiate- 



