680' mkIf. chapman on the bargate beds of surrey. [Nov. 1894/ 



• : " Felspar. These grains are mostly kaolinized. 

 "A few glauconite- grains also occur. 



"' The minerals present here are of the same size as those from the 

 Bagshot Sands, and three times as large as those from the Chalk- 

 marl of the Isle of Wight." 



Overlying the layer of clay-with-pebbles is a band of finely lami- 

 nated sand, with many small pebbles and occasional thin seams of- 

 clay (also containing microzoa) ; the thickness of this band is about 

 9 inches. Together with the pebbles in clay below, it is conspicuous 

 in the quarry section, because of its greater resistance to weather- 

 ing. Above these comes in a bed of pale current-bedded sand, 

 averaging 3 feet in thickness. 



This is overlain by a whitish siliceous bed of variable thickness, 

 consisting of sponge-remains, including fragments of Lithistid 

 sponges, together with detached spicules of other types. 



The higher beds in the Littleton Quarry consist of pebbly sand 

 with rolled fossils, and sandy strata alternating with layers of com- 

 pact and generally ferruginous Bargate limestone, amounting 

 altogether to about 18 feet. The lower portion of these beds is 

 merely a loose calcareous grit, in the higher it is an exceedingly 

 compact limestone. The harder rock is of a dark reddish-brown 

 colour. On a fractured surface this rock shows numerous cleavage- 

 surfaces of calcite, shell-fragments, and bright-green glauconitic 

 particles. 



In thin sections under the microscope the compact Bargate Stone 

 is seen to consist of numerous rounded and subangular quartz-grains, 

 chalcedony, a few scattered grains of glauconite, many fragments of 

 shells such as Terebratulce and Exogyrce, nearly all of which have 

 been silicified, also traces of polyzoa, portions of Lithistid and 

 Hexactinellid sponges, i.nd numerous spines and other parts of 

 echinoderms. These are all firmly cemented together by a ferrugino- 

 calcareous matrix. The molluscan shell-fragments are often perfo- 

 rated by apparently two distinct species of boring algae, one 

 consisting of fine interlacing filaments, and the other of coarser per- 

 forations with branches at short intervals. Moreover, in thin sections 

 of the limestone, teeth and bones of fish, etc., and occasionally the 

 tests of foraminifera can be distinguished. Amongst the latter 

 are Te.vtularia trochus, d'Orb., Gaudryina, sp., and Lagena Icevis 

 (Mont.). 



After dissolving this rock in weak hydrochloric acid, the residuum 

 amounts to 65 per cent. The rock thus acted upon is, however, 

 still cemented together by ferruginous material; and this, when 

 removed by boiling in strong hydrochloric acid, is found to amount 

 to 12 per cent. 



Some of the bodies in the siliceous residue resemble the spines of 

 certain species of Hemipedina and Cidaris from the Middle and 

 Upper Oolite, but the Bargate specimens are very minute. 



The chalcedonized sponge-spicules are of a pale bluish-grey colour, 

 With a surface similar in appearance to ground-glass. There are 

 many examples of distortion amongst the casts of the axial canals of 



