A. J. Jukes-Browne—The Subdivisions of the Chalk. 251 
a matrix of glauconitic marl, which passes up into grey marly chalk, 
that four-fifths of the fossils found in it have been derived from the 
Gault, and that the fauna of the bed itself certainly belongs to that 
of the Chalk Marl. 
2. Chalk Marl or Zone of Rhynchonella Martini.—This consists of 
hard greyish marl below, passing up into softer and more argillaceous 
bluish-grey marl; the whole being about 60 feet thick. It is not 
very fossiliferous, and only 20 species have yet been collected from 
it; 14 of these occur also in the Greensand at its base, but Ammonites 
varians and some other species appear for the first time in its upper 
beds. It is a remarkable fact that Rhynchonella Martini has never 
yet been detected in the Cambridge Greensand, where its place is 
taken by a variety of the allied species, Rh. lineolata; this latter 
does not seem to occur in the overlying marl, and is only known 
elsewhere in the Neocomian Clay of Speeton, and the Red Rock of 
Hunstanton. Another little Brachiopod, found abundantly in the 
Greensand and also in the Chalk Marl, is a minute variety of 
Terebratulina striata, recently named T. triangularis by Mr. Etheridge. 
This has hitherto been considered a variety of Z. gracilis, and is in 
some respects an intermediate form between the two species. I 
believe the same variety occurs also in the Hunstanton rock. 
3. Totternhoe Stone.—At the base of this division there appears to 
be a more or less continuous layer of green-coated calcareo-phosphatic 
nodules, which were first described by Prof. Hailstone in 1816." 
The stone above is a compact grey sandy limestone, in beds about 
2 or 3 feet thick, and having a total thickness of from 12 to 16 feet. 
The best exposure to be found in Cambridgeshire is at Burwell, 
where it is largely quarried for building stone, and where it has - 
yielded a large number of fossils. There is a good collection of 
Burwell stone fossils in the Woodwardian, and the fauna now 
known is a large one, numbering from 80 to 90 species. 
Mr. Etheridge has described several new forms, and two of these, 
Lima echinata and Pecten fissicosta are very characteristic of the 
horizon; many other fossils are much more common, such as 
Rhynchonella Mantelliana, Kingena lima, Pecten opercularis and 
Lima globosa, but these occur also in the beds above and below. 
Cephalopoda and Gasteropoda are here particularly abundant, 
Ammonites varians and Am. cenomanensis may be specially mentioned 
as frequently met with. Holaster subglobosus has not yet been 
found at Burwell, where Hemiaster Morrisi, appears to take its place, 
but the former has been found in the basement bed elsewhere. 
4. Zone of Holaster subglobosus.—At Burwell the upper limit of 
the Totternhoe Stone is marked by a bed of hard sandy rock, known 
locally by the name of “bond,” but elsewhere the line of division is 
not so clear; the chalk, however, quickly becomes less sandy, and of 
a yellowish or creamy-white colour, passing up into a tough but 
nearly pure white chalk. In this division the planes of bedding are 
very indistinct, and the mass splits along curved lines, which 
produce an appearance of irregular and lenticular bedding. Fossils 
1 Trans. Geol. Soc. vol. iii. p. 243. 
