TF. J. Sollas — Green Grains in the Cambridge Greensand. 543 



progressive growtb. in the glauconite from the exterior inwards, 

 while in fact no signs of any such increase can be detected, neither 

 in successive incrustations, nor in any crystalline arrangement, like 

 that which one observes when a mineral infiltration has really taken 

 place in this stalactitic manner. 



The glauconite is indeed not crystallized, but simply cryptocrystal- 

 line, in exactly the same way as flint and coprolite are crypto- 

 crystalline. Accepting then, as seems to be generally allowed, that 

 the presence of animal matter has been one of the essential deter- 

 mining causes for the deposition of glauconitic material, we have 

 next to find animal matter for this purpose. The inclosed Forami- 

 nifera seem too minute to have furnished a sufficient supply, nor 

 have they been proved to be constantly present in the granules, 

 especially since the sections of many of the latter show no signs of 

 them : it thus appears that we must have recourse to the agency of 

 such minute and soft-bodied organisms as are to be found amongst the 

 Protista and Protozoa ; these scattered throughout the Chalk-marl in 

 which the green grains were originally formed would, on their 

 death, lead to a deposition of glauconite about themselves, and thus 

 necessarily include the immediately adjacent Foraminifera and 

 coccoliths, and the other bodies which they now contain ; while the 

 shape of the resulting glauconitic mass would be simply determined 

 by the irregular extension of the decaying organic matter. 



The resemblance of the glauconitic granules to flints and copro- 

 lites, which appears on this view, is very striking. Both flints and 

 coprolites are found filling the interior of certain shells, most notable 

 instances of which are the coprolitic casts of Fleurotomaria, and the 

 flint which fills the interior of Ananchytes ; both frequently surround, 

 even to the extent of inclosing, the organisms, which at other times 

 they simply occupy as casts ; and both also have served to mineralize 

 the soft animal matter furnished by various kinds of sponges ; the 

 glauconitic granules similarly are frequently confined to the interior 

 of foraminiferal tests, from which, however, they sometimes extend 

 so as to spread over the exterior and form a complete in closure, 

 while finally, according to our view, they present a further analogy 

 in that they have also formed about the soft bodies of decomposing 

 animals, of the previous existence of which they now supply the 

 only trace. 



EXPLANATION OF PLATE XXI. 



Fig. 1. Section of a glauconitic granule, magnified 140 diameters; (/) included 



Foraminifer ; {g) granules ; (m) fragment of crystalline mineral. 

 Fig. 2. Section of a glauconitic granule, including a part of a Foraminifer (/) ; 



the rest of which is cut off by the edge (/). ( x 140.) 

 Fig. 3. Section of a glauconitic granule, magnified 435 diameters; {d) coccoliths; 



(c) coccosphere; (s) splinter of uncertain nature. The other letters as 



in Fig. 1. 

 Fig. 4. Part of the polygonal reticulation of which one of the green granules is 



composed, (x 435.) 

 Fig. 5. Simple form of coccolith ; {a) the outer annulus ; (c) the clear zone ; 



(.s) the clouded central area; [g) the central granule. 

 Fig. 6. Coccolith with marginal grove, seen face on, but slightly tUted at one end ; 



(6 a) side view of the preceding. 



