138 MESSRS. A. J. JUKES-BROWNE AND W. HILL : [May 1 896, 



Base of the Middle Chalk. 



Specimens from Lyme Eegis, Bindon, Beer Head, and Branscombe 

 show that the usual change takes place, and that the compact 

 glauconitic chalk at this horizon consists chiefly of spheres thickly 

 packed in the fine calcareous material of the matrix. Globigerince 

 are among the most common foraminifera, but are not very abun- 

 dant, and the shelly fragments consist chiefly of Inoceramus-])Yisms. 

 Large quartz- and glauconite- grains still characterize the deposit, 

 but they pass away in about 3 feet, and the rock has then the 

 usual characters of Middle Chalk. 



The Upper Greensand (or Gaize) . 

 Cape La Heve. 



For the purposes of this paper it is only necessary to describe 

 the minute structure of the upper part of the Upper Greensand 

 (the Gaize) in order to show that the material of which this 

 division is composed differs considerably from that of the overlyiDg 

 Cenomanian. 



Viewed under the microscope in thin sections, the matrix of the 

 Greensand is seen to consist largely of fine, amorphous, siliceous 

 matter, probably silicate of alumina, intermingled with which are 

 minute calcareous particles. There are very few foraminifera, and 

 not many shell-fragments or sponge-spicules. Globules of colloid 

 silica are present, but not abundant. The proportion of quartz- 

 sand is large, but the grains are small and angular ; mica-flakes may 

 be recognized. Bather large grains of glauconite are common, but 

 not abundant. The rock compares well with a specimen of the 

 upper part of the Upper Greensand of the Isle of Wight, taken 

 from Culver Cliff, except that the grains of quartz and glauconite 

 are distinctly larger. 



Isle of Wight. 



At the top of the Upper Greensand grains of glauconite become 

 very abundant, and these and the quartz-grains are coarser, and the 

 rock more calcareous. Specimens from Beds 2, 4, and 5 (see p. 105) 

 from Collins Point show distinctly the commencement of a transition 

 from Upper Greensand conditions to those of Chalk Marl. 



The Cenomanian of France. 



The Chloritic Marl of Cape La Heve. 



The bed containing many black phosphates, which we take as 

 the equivalent of the Chloritic Marl, will not compare in its minute 

 structure with that of the Isle of Wight. It is a less calcareous 

 deposit, it contains more fine inorganic material, and the grains of 

 quartz and glauconite are more numerous and larger ; indeed, as 

 already mentioned on p. 121, some of the former are small pebbles. 

 There is a little colloid silica, but few sponge-spicules, shell-frag- 

 ments, or foraminifera. 



