338 REPORT— 1897. 



all in the state of casts and impressions. In no case does any actual shell 

 or test remain, but the firmness of the rock has in most cases prevented 

 the enveloping matrix from being pressed down on to the internal cast, so 

 that the external cover generally retains the shape and impression of the 

 original shell, and a mould can, if necessary, be taken from it. The 

 fossils had been carefully collected, and as both casts and covers had been 

 transmitted, it has been possible to determine many of the species. 



Before discussing the species, however, the rock itself merits descrip- 

 tion, for its peculiar characters seem to have escaped previous observers. 

 To the eye it presents itself as a very fine-grained siliceous rock, resem- 

 bling malmstone, dark grey when damp and freshly broken, drying to a 

 lighter grey. Fractured surfaces often show spots and patches of darker 

 material than the rest of the mass. Under the lens it showed a finely- 

 granular matrix, containing many small grains of glauconite, and numerous 

 flakes of mica, with small patches of a yellowish-green mineral which is 

 apparently a decomposition product. 



The general aspect and light specific gravity of the rock led me to 

 suspect the presence of colloid silica, and accordingly I sent specimens to 

 Mr. W. Hill, F.G.S., for microscopical examination. Mr. Hill cut slices 

 from two of these, and furnishes me with the following account of the 

 structure exhibited by them : — 'The material of both slides is alike, and 

 compares most nearly with the micaceous sandstone of Devizes (Upper 

 Greensand). The ground mass consists of amorphous and semi-granular 

 silica, neutral to polarised light, with little or no calcite. There ai'e 

 many sponge spicules, the walls of which have mostly disappeared, but 

 which are outlined in the matrix. The space once occupied by the spicule 

 is often partly filled with globules of colloid silica, like those described 

 by Dr. Hinde in malmstone, and similar globules are dispersed through 

 the mass of the rock. There is much quartz sand in small, angular, even- 

 sized grains, but not so much as in Devizes sandstone. Glauconite grains 

 are also abundant, but the quantity varies much in difierent parts of the 

 rock ; the grains seem to be breaking up, and are often seamed with vein- 

 like markings. There are also larger patches of dirty-green material, 

 which has a somewhat indefinite outline, and may be of secondary forma- 

 tion. Small flakes of mica are scattered through the slides, but it is only 

 when these are cut transversely that the mineral can be easily identified.' 



From the above description it will be seen that the rock may be 

 termed a gaize — that is, a fine-grained sandstone, in which colloid silica is 

 an important ingredient ; this is not a common rock, and in England it is 

 only known as occurring in the Upper Greensand in association with 

 malmstone. In France a gaize of Lower Gault age, containing Ammonites 

 mammillaius and Ajn. interruptus, occurs in the Ardennes (Draize), but I 

 can find no record of the rock occurring in the Lower Cretaceous series 

 either in France or Germany. 



The formation of gaize and malmstone probably took place in clear 

 water of a moderate depth ; it is not a shallow water deposit, and yet it 

 was deposited within the range of a current which carried fine sand. The 

 abundance of sponge spicules shows that the conditions were such as to 

 favour the growth of siliceous sponges. 



Remarks on some of the Fossils. 



The collection sent to me includes some species which have not 

 yet been recorded from the Moreseat rock, and as these are all Lower 



