542 W. J, Sollas — Green Grains in the Cambridge Greensand. 



8, 9, 10, the stalk is produced from the centre of the transverse 

 thickening ; of these stalked varieties only forms like Fig. 15 have 

 been observed in the green grains. (See PI. XXI. Fig. 3 dJ.) 



Fig. 19 is a variety of Fig. 9, differing from it by its granulated 

 edge; Fig. 16 is a stalked form, granulated sharply on its upper 

 margin, so as to resemble a crown-wheel. 



Coccospheres. — These I have observed in several instances in the 

 Chalk-marl as spherical bodies covered loosely with the oval form of 

 coccolith like Fig. 5. On solution a faint granular membrane cor- 

 responding in outline and size with the original sphere remains 

 behind ; it stains faintly with magenta. In the glauconitic granules 

 I have several times noticed small spherical bodies with thin walls, 

 marked with refractile ridges and granules, which closely resemble 

 coccospheres ; the best marked of these is shown in Fig. 3 at c. 



Granules. — These bodies, which are exactly similar in size and 

 appearance to those which make up so large a proportion of the 

 Chalk-marl, and which resemble also the refractile granules inside 

 the coccoliths, occur very abundantly in the green grains, and can 

 be distinguished therein by their greater transparency and different 

 refractive index. 



Bodies of uncertain nature. — Small angular fragments of colourless 

 and transparent crystalline minerals resembling felspar, splinters of 

 an indeterminate substance, bacilli and other small bodies, are some- 

 times inclosed. One green grain ^o'^ diameter was observed to be 

 entirely filled with a faintly defined, fime, polygonal reticulation, a 

 part of which is shown, magnified 435 diameters, in Fig. 4. What 

 this may be it is hard to say ; but clearly the organism from which 

 the grain was derived had no connexion with the Foraminifera. 



Conclusion. — The coccoliths and granules which characterize the 

 green grains of irregular form, are also present in the glauconite casts 

 of foraminiferal chambers, and in the phosphatic material and crystal- 

 line calcite, which occupy the interior of the foraminiferal tests; 

 while all the bodies described from the > interior of the granules 

 occur also in the phosphatic matrix of the coprolite which imbeds 

 both the foraminifera and the green grains, and in the Chalk-marl 

 which contains the coprolites. The character, in fact, of the irregular 

 granules and of the foraminiferal casts is that of Chalk-marl, 

 which has become changed by a mineral replacement into glauconite. 

 What the cause is which has induced this change is another question, 

 but apparently the presence of organic matter in some form or other 

 has been essential to it; thus we frequently find glauconitic material 

 forming a cast of the interior of a foraminifer and infiltrating 

 its tubules, without in the least affecting its calcareous walls, which 

 retain their original composition. It here then occupies the place of 

 animal matter to the total disregard of the associated mineral shell. 

 To this it may be objected that the glauconite may also be regarded 

 as occupying a space separated from the external Chalk-marl by a 

 limiting foraminiferal test, and that the presence of this separation 

 was sufficient to bring about the infiltration which has taken place ; 

 but if this view be true, one would expect to find some trace of a 



