Vol. 57.] UPPER GEEENSAND AND CHLOKITIC MAEL OP WILTSHIRE. 105 



parts being darker and more chalcedonic. Examination with a lens 

 shows that it is full of sponge-spicules, which seem to have formed 

 a matted mass of organic silica entangling some fine quartz-sand. 

 Subsequently there was a partial solution of the colloid silica, some 

 of it being redeposited in the central parts of the bed in a form 

 which passed into chalcedony. 



Bed 8 is a fine-grained, greyish, glauconitic spiciiliferous 

 silt, resembling the material of Bed 5. It consists largely of broken 

 sponge-spicules and globular silica, this matrix appearing to the 

 unassisted eye as a white floury matter ; there is also much fine 

 quartz-sand, many scattered grains of glauconite, and flakes of 

 silvery mica. Tests of arenaceous foraminifera are common iu 

 this bed, but only a few fossils have been found, namely : — 



Avicula gryphcBoides. 



Pecten asper. 



Ostrea canaliculata (?). 



Serjpula anmdata (?). 

 Cardiaster fossarius (crushed). 

 Siliceous sponges. 



Bed 9 is a curious and interesting rock. Parts of it consist 

 almost entirely of large broken sponge-spicules, cemented into a 

 granular limestone by crystalline calcite ; but the portions between 

 these indurated lumps consist of. glauconitic sand, both quartz 

 and glauconite being in fairly large grains. With them, however, 

 is much sponge-debris ; therefore the rock may be called a 

 calcified sponge-rock, and it shoAvs that sponge-rock does not 

 always give rise to chert. 



Bed 10 is a hard calcareous and spiculiferous sand- 

 stone with a granular texture. It is the lowest bed actually 

 quarried, but a small excavation made below it showed a few 

 inches of greenish-grey sand enclosing small lumps of cherty stone. 



Mr. Holbrook, of Maiden Bradley, who has worked in several of 

 the quarries and has assisted in sinking wells in the village, informs 

 us that beds containing flinty cherts occur to a depth of at least 

 12 feet below the bed of sandstone (No. 10) ; and further, that they 

 include two beds of hard sandstone, formerly quarried for building- 

 stone, of which the church and the older houses iu the village have 

 been built. Mr. Holbrook has given us the following as the general 

 succession below the floor of the existing quarry at Maiden-Bradley : 



Feet. Inches. 



Hard sandstone with shells [Neithea quadricostata\ 2 



Layer of green sand 9 



Sand with lumps of 'ruckly' flint [chert] 4 3 



Very hard sandstone 1 3 



Sand with ' rnckly ' flints 4 



Hard sandstone with shells 9 



Green sand 10 



Hard sandstone- rock 2 



Sand, proved for 30 



This would make the total thickness of beds containing chert 

 about 24 feet. Part of the foregoing succession is confirmed by the 

 section next to be described. 



