294 PEOCEEDINGS OP THE GEOLOGICAL SOCIETY. [April 24, 



Gymjne Fossiliferous Tufa. . 



Analysis, 



Per cent. 



Silica 43-150 



Alumina 21-570 



Perric oxide 3-610 



Ferrous oxide 8-520 



Lime 12-450 



Magnesia 1-785 



Soda 1-710 



Potash 1-310 



Carbonic acid 3-560 



Water, constitution 1-100 



Water, hygroscopic 0-500 



99-265 



Insoluble in hydrochloric acid, 45-100 per cent. 



Silica 60-753 



Alumina 19-395 



Eerrous oxide 4-800 



Lime 7-206 



Magnesia 1-873 



Soda 3-791 



Potash 2-904 



100-722 



Soluble in hydrochloric acid, 54-900 per cent. 



Silica . 28-234 



Alumina 23-442 



Ferric oxide 6-575 



Ferrous oxide 11-666 



Lime 16-074 



Magnesia 2-022 



Carbonic acid 6-484 



Water, constitution 2-003 



Water, hygroscopic 0-910 



97-410 



Mr. AUport, of Birmingham, has examined sections of these ana- 

 lyzed rocks under the microscope, and thus describes them : — 



Of the cri/stcdlme rode he says : — 



" This is a diorite, containing hornblende, triclinic felspar, ortho- 

 clase, a little brown mica (biotite) and pyrites. 



" Many of the minerals are impei-fectly crystallized. 



" The crj'stals of felspar showing bands of colour or striae, when 



