540 W. J, Sollas — Green Gtmns in the Cambridge Greensarid, 



The substances usually scattered tlirougliout tlie sections are small 

 Foraminifera, Coccoliths, Coccospheres, minute granules, fragments 

 of crystalline minerals, and other substances, the nature of which is 

 uncertain. 



Foraminifera. — These are very small, and in proportion to the 

 size of the granule containing them absolutely insignificant (PL XXI. 

 Fig. I/.)- The walls of their tests are either well preserved as 

 pseudomorphs in glauconite, in which case they are of the same 

 green colour, but clearer and more transparent than the surrounding 

 material, and well defined on both their inner and outer margins ; 

 or else they have disappeared altogether or in part, leaving only a 

 few granules or a dark brown line to mark their original position. 



The position of the Foraminifera in the green grains is very 

 variable, sometimes a test may be seen in the middle of a section 

 (PI. XXL Fig. 3 /.), but quite as often at the side (PI. XXI. Fig. If.); 

 whilst in one instance (PL XXL, Fig. 2/.) the outline of the grain 

 intersects the inclosed Foraminifera, cutting off the interior from an 

 exterior portion which has since disappeared. The intersecting edge 

 of this grain (I.) is, however, a suspiciously straight one, and may 

 possibly be due to fracture. 



Xo appearance of a crystalline radiation from any of the included 

 bodies towards the circumference of the granules is to be detected 

 either with ordinary or by polarized light. 



CoecolitJis-. — The Chalk-marl, which constitutes the greater part 

 of the Cambridge Greensand bed, is to a great extent composed of 

 coccoliths, entire and fragmentary, which in the number and variety 

 of their forms surpass all that I have yet seen figured from recent 

 seas. I have already drawn, and partly described, a large series of 

 these bodies ; but as it will be impossible to publish the description 

 for some time, and as their presence in the glauconite granules is a 

 subject which concerns us now, it may not be amiss to give a brief 

 preliminary account of the forms which have been recognized in the 

 granules, supplemented by the addition of one or two others from 

 the Chalk-marl. 



The form represented in PL XXL Fig. 5, is one of the most abun- 

 dant in the Chalk-marl, and occurs most commonly in the glauconitic 

 granules. It consists of a transparent, colourless or faintly greenish 

 oval ring (Fig. 5a.), well defined on its outer and inner circum- 

 ference, inclosing an oval space, clear and transparent (c.) at its 

 outer margin, close to the inside of the ring, but cloudy and 

 granular (s.) towards the centre, at or near which is situated a single 

 granule (g.), larger than the rest, transparent and of the same green 

 tint as the outer annulus. "Viewed sideways this form appears like 

 a simple rod. 



,The whole of this structure consists of carbonate of lime, and on 

 solution in weak acid dissolves entirely or with the exception of 

 a delicate membranous film, which is dotted over with a number 

 of faintly marked granules ; and which on the addition of carmine 

 or magenta stains to a light red colour. Fig. 20 represents such a 

 film left on the solution of a form like that shown in Fig. 8. 



