Cretaceous Fossils found in Aberdeenshire. 27 



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 

 description, for its peculiar characters seem to have escaped previous 

 observers. To the eye it presents itself as a very fine-grained 

 siliceous rock, resembling 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 decom- 

 position 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 

 polarized light, with little or no calcite. There are 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 in 

 malmstone described by Dr. Hinde,^ and similar globules are 

 dispersed through the mass of 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 different 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 formation. 

 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 mammillatns and Am. interriiptus, 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 



1 Phil. Trans. Eoy. Soc. 1885, pt. ii, p. 403. 



