504 MESSRS. WHITAKER AND JUKES-BROWNE ON [Aug. 1 894, 



423, 427. Very hard, creamy-white chalk, like the more solid parts 

 of the Melbourn Rock. This is confirmed by the examination 

 of a slide prepared by Mr. Hill from 427, which has the 

 structure of the lower part of the Melbourn Rock. 



430. A soft, greyish, marly chalk. Of this Mr. Hill reports that it 

 presents a marked contrast to the preceding, and resembles the 

 marly chalk of the Belemnitella plena-zone near Hitchin. 



443, 470, 476, 500. Firm greyish-white chalk, 443 being rather 

 hard, the others softer ; 500 is as white as 443. 



510, 511, 512. Soft grey chalk. 



517, 525. Rather hard grey chalk. 



530, 550, 556, 558. Rather hard grey Chalk Marl. 



569, 579. Firm grey Chalk Marl. Having cut slides from both, 

 Mr. Hill writes that they are characteristic Chalk Marl, a 

 certain amount of fine siliceous matter being present in the 

 calcareous mud of the matrix. 569 is rather sandy and shelly, 

 the shell-fragments being large for Chalk Marl. 579 is less 

 sandy and shelly. Glauconite-grains are common, but small 

 in 569 ; larger in 579. 



585. A rather hard, grey, sandy and micaceous chalk. Abundant 

 flakes of white mica and minute glauconite-grains can be seen 

 with a lens. Mr. Hill describes this as containing " much 

 inorganic matter, fine quartz-sand to a large extent replacing 

 the shell-fragments of the chalk, and still finer argillaceous 

 matter preponderating over the calcareous material in the 

 amorphous matrix. There is much glauconite in small grains, 

 but these are larger and darker than those in the overlying 

 beds, marking an approach to the Greensand. A number of 

 foraminifera and a few calcareous spheres occur.'' 



587, 588. Greenish, sandy, glauconitic and micaceous marl. In 

 microscopic structure this might be called Greensand, as both 

 quartz and glauconite-grains are abundant and of fair size ; but 

 there is still a considerable amount of amorphous calcareous 

 matter. Mr. Hill writes that it much resembles a slide from the 

 base of the Chalk Marl near Tring, believed to have come from 

 Ivinghoe, but is rather coarser in grain. It may therefore be 

 regarded as a fine-grained variety of Chloritic Marl. 



590 ? The depth-label of this sample has been lost, hut we think the 

 sample must have come from here, for it is a dark-grey sandy 

 marl enclosing large grains of quartz and of glauconite, and con- 

 taining patches of darker and more sandy material ; also two 

 nodules of dark grey phosphate and several fossils (Pecten inter- 

 striatus, P. orbicularis, a small oyster, and many broken frag- 

 ments of Inoceramus). It resembles the representative of the 

 Cambridge Greensand formerly worked at Sharpenhoe in Red- 

 fordshire. 



591, 592, 604. Fine-grained, grey, marly, glauconitic and micaceous 

 sandstones, 592 containing a light-brown phosphatic nodule. 

 These much resemble the very fine-grained micaceous sand- 

 stones of the Upper Gault or Upper Greensand in Rucks, where 

 the so-called Upper Greensand is thinning out. All are rather 

 heavy in the hand. 



