1^ ME. E. WETHERED ON Ilf SOLUBLE EESIDUES EKOM 



jSTo. 4. Eolled detrital quartz-grains measuring as much as -015 

 of an inch in diameter. Chalcedonic sponge-spicules and other 

 fragments of silica in the same form, among which are casts and 

 spherical objects measuring about -015 of an inch in diameter. 



'No. 5. Chiefly microscopic crj-^stals with nuclei and fragments of 

 chalcedonic sihca. The nuclei of the crystals are undoubtedly 

 detrital quartz-grains, and the crystals have been formed by the de- 

 position of secondary silica upon the surfaces of original quartz- 

 crystals, as described by Dr. Sorby, F.R.S. * 



Xo. 6. Detrital quartz, some tourmaline, chalcedonic silica, and 

 pyrites. 



1^0. 7. Oolitic limestone ; residue consists of detrital quartz and a 

 very little chalcedonic silica. 



jSTo. 8. Detrital quartz, on the surface of which secondary silica 

 has been deposited, and in some cases a perfect crystal has formed 

 around a quartz-grain as a nucleus. Some of the micro-crystals 

 are very perfect and larger than previously observed, one of which is 

 represented in Plate YIII. fig. 3 A, and measures -015 X '009 of an 

 inch. There is also present a considerable quantity of chalcedonic 

 silica. 



No. 9. Chiefly micro-crystals measuring -007 x "003 of an inch, 

 with detrital quartz-grains as nuclei ; also detrital quartz-grains 

 which are not entirely enveloped in a deposit of secondary silica. The 

 crystals are especially important, as besides the inorganic nuclei, 

 they contain the minute globules seen in amorphous silica, which 

 points to the conclusion that the secondary deposit was derived 

 from amorphous and chalcedonic silica associated with the detrital 

 quartz in the limestone. 



]S"o. 10. Masses of amorphous and chalcedonic silica, some of 

 which are crystallized around the edges. In some instances portions 

 represent three stages of structural transition ; the centre portion is 

 amorphous and is surrounded by chalcedonic silica, and this, again, 

 passes into the crystalline condition (see woodcut, p. 194). There 

 are also micro-crystals : some of these have detrital quartz-nuclei, 

 but in others it is difficult to make out any nucleus at all, with the 

 exception of a minute globular structure similar to that seen in 

 amorphous organic silica. 



No. 11. Chalcedonic and amorphous silica, some of which appears 

 to be casts. A few grains of detrital quartz, tourmaline and zircon. 

 Some nucleated crystals also present. 



No. 12. Micro-crvstals with detrital quartz-nuclei, averaging about 

 •003 X -007 of an inch in size (Plate VIII. fig. 4). 



No. 13. Clusters of micro-crystals without recognizable inorganic 

 nuclei. Apparently the objects are crystallized chalcedonic silica. 



No. 14. Brown siliceous fragments, which seem to be casts or 

 pseudomorphs. Small pieces of chalcedonic silica ; detrital quartz 

 and micro-crystals with inorganic nuclei. 



No. 15. Fragments of chalcedonic silica, among which are casts 



* Presidential A-dclress to the Geological Society, February 1880, p. 62. 



