Floor of the English Channel. 67 



the dissolution of siliceous spicules, that the Foraminifera are in 

 rather greater number and variety, and that there is a larger 

 proportion of small shelly particles in the matrix, exhibiting much 

 variety of outline as if derived from several different kinds of 

 organisms. On the other hand, the Cuvieri beds generally contain 

 spherical areas, filled with amorphous matrix, which represent the 

 spaces once occupied by Radiolaria, while in the higher zone such 

 spheres are absent or very rare. 



It should also be mentioned that the ordinary chalk of both zones 

 has a miich less variety of contents, that of the Cuvieri zone generally 

 containing much Inoceramus debris but few spicules, while in the 

 cortestudinarium zone the reverse is the case. Moreover, in the latter 

 tliere is generally a larger proportion of amorphous matrix with fewer 

 cells and spheres. It is only in the liard rocky layers occurring 

 in that zone in Dorset and Devon that cells and spheres are so 

 abundant. 



When the slices cut from the pebbles 41, 58, and 72« are compared 

 with those above-mentioned it is seen that they bear a rather greater 

 resemblance to those from the beds in the Cuvieri zone than to 

 those from the cortestudinarium zone. Tliey differ, however, from the 

 former in the absence of any traces of Radiolaria, and also of course 

 (as previously mentioned) in the presence of large fragments of 

 Polyzoan zoaria. It is possible that these two points of difference 

 explain one another, and that the chalk of the pebbles was formed in 

 a locality where Polyzoa were abundant and Radiolaria did not exist, 

 while a little further north the conditions were unfavourable for 

 Polyzoa but lay in the track of a current carrying Radiolaria. 



The only true chalk which I have found to contain much debris of 

 Polyzoa is a bed of yellowish rocky chalk forming the base of the 

 Cuvieri zone in a quarry near Branscombe Church between Sidmouth 

 and Beer. This bed differs from, the basement bed seen in the cliffs 

 by the absence of quartz and giauconite grains, its general composition 

 resembling that of the pebbles 41 and 58 and including several 

 fragments of Polyzoan framework, but it differs in containing a much 

 larger quantity of Inoceramus debris and in the greater abundance 

 of large sponge spicules, as well as by including many casts of 

 Radiolaria. 



The pebbles have no resemblance to the ' Beer Stone ', which is 

 a coarse shelly limestone composed mainly of fragments of Inoceramus 

 shell, nor to the beds which overlie that stone in Beer Quarries, which 

 are all very shelly, even the highest compact rock-bed being full of 

 Inoceramus and Echinoderm fragments. 



Pebble 35 differs from the others in having a much larger proportion 

 of amorphous matrix, with fewer cells and spheres and a greater 

 number of sponge spicules. There is, moreover, a greater number 

 of Poraminifera and more variety of small shelly fragments In all 

 these respects it more nearly resembles the ordinary nodular chalk 

 of the cortestudinarium zone, but it contains in addition fragments of 

 a cellular skeleton like that of Polyzoa. 



The pebbles 17 and 25, so far as the characters of the component 

 chalk can be discerned in the small areas which remain, are of similar 



