1872.] SOXLAS CAJIBRIBGE UPPER GEEENSAND. 399 



Bairdla suhdeltoidea ; CijthereUa truncata ; Cyihere punctatula, C. 

 umhonata, and others. C. umhonata has not been found before below 

 the Chalk-marl. 



(2) Siliceous sand. — Small grains of coloured quartz, obsidian, 

 grit, and other rocks form a smaU proportion of the Greensand, 

 Foraminifera of arenaceous habit often imbed these grains in their 

 tests. 



(3) Glauconite and Phospliate Grains. — The phosphate grains 

 consist of coprolitic debris, coprolitic casts of Poraminifera, and small 

 ovuloid granules and cylinders of unknown derivation. 



The glauconite grains are the casts of Poraminifera, possibly 

 also of other minute shells. The larger casts, about ^y to -^" 

 in diameter and less, are marked into projecting lobes by deep 

 sulcations, generally lined at the bottom with white calcareous 

 matter, which serves to mark out the limits of each lobe. These 

 forms are derived from Textularia, Lituola, and Bidimina ; in size 

 they correspond very closely with such a derivation, just passing 

 through the meshes of a sieve which retain almost all the numerous 

 Bidiminoi mingled with them. Each lobation of the cast corre- 

 sponds to the interior of a chamber of the Foraminifer ; and each 

 white calcareous line between the lobes is the edge of the septum 

 which once separated adjoining chambers, and now, in some eases, 

 extends inwards between their casts. This is shown by sections 

 made in various directions through the green grains. Wlien one of 

 these sections of glauconite is viewed with polarized light, distinct 

 colours are obtained ; with parallel prisms, dark green ; and a bright, 

 lighter-coloured green, with crossed prisms. Sometimes Bulimince 

 are met with having part of their shell worn away, revealing a 

 green cast within. Besides the above, other forms are found as casts 

 in the sand — Orthocerina, numerous elongated triangular pj^ramids 

 (rarely constricted into definite lobes), Rotalia, one or two minute 

 Nodosarice, small fusiform casts from Lagena, and distinct Glohige- 

 rmrt-casts. Minute globules yuVo" ^^ Too"" ™ diameter, occur plen- 

 tifully the smaller ones are probably detached spheres from Glohi- 

 gerina-casts, and the larger ones casts of chambers broken off from 

 other Foraminifera, as Bidimina ; frequently glauconite may be 

 seen through the worn-away shell of such chambers. Globigerina, 

 Botalina, and various pseud-arenaceous forms sometimes show green 

 casts in their interior. From the resemblance of most of the green 

 grains to the Foraminifera found with them, from their rough 

 parallelism in size, from the appearance of many of the grains when 

 sections are made of them, and from the occurrence of giauconite- 

 casts in the interior of the original Foraminifera, we must attribute 

 to the green grains a Foraminifera! origin. That this has not been 

 determined by previous observers is partly due to the use of acid, 

 after Ehrenberg's directions, in preparing the sand ; this of course 

 would obliterate the calcareous lines which distinguish the lobations. 

 The silica and various silicates mingled with the glauconite grains 

 must have thrown the analysis of these grains hopelessly wrong. 



