A HISTORY OF BEDFORDSHIRE 
The Totternhoe Stone has yielded at its headquarters numerous 
organic remains. Of these it may suffice to mention the crushing teeth 
of the fishes Prychodus polygyrus, P. latissimus, P. decurrens, and P. mam- 
milaris, the cephalopod Nautilus atlas, and the lamellibranch Pecten orbicu- 
Jaris, specimens of all of which are in the museums of Luton and St. 
Albans. Another exposure occurs in the Midland Railway cutting at 
Chalton, where it is visible on the face or the excavation when viewed 
from the bridge which carries the road to Sundon. This section has 
furnished Pecten fissicosta, P. orbicularis, Ammonites varians, and several 
fine examples of Nautilus elegans, the largest of which, about 8 inches 
in diameter, is now in the Woodwardian Museum, Cambridge. 
Overlying the Totternhoe Stone is a tough grey blocky limestone, 
the zone of Ho/aster subglobosus, which in some of its exposures has a 
yellowish tinge at the base, doubtless due to the presence of iron oxide. 
In its passage upwards it becomes light grey or white. The lines of 
deposition are indistinct, and it was evidently laid down under tranquil 
conditions. Its mineral composition and fossil contents indicate that 
there was a gradual increase in the depth of the sea during its deposi- 
tion; one result of which was that many of the genera of Mollusca 
which previously existed died out or migrated to other districts and were 
succeeded by others which were adapted to the altered conditions. The 
stratum contains a high percentage of lime, this material averaging at 
least three-fourths of its bulk. There is also present a small amount of 
silica, both organic and inorganic, the former consisting of sponge- 
spicules and the latter of siliceous granules. Oxide of manganese is 
often present in the form of a fine black deposit on the surface of the 
blocks into which it separates during weathering, as well as distributed 
unequally through the mass. 
The fossils of this division of the Lower Chalk are both numerous 
and interesting. Conspicuous amongst them are the palatal teeth of 
several species of Ptychodus, and the pointed teeth of Lamna, Corax, and 
Notidanus, the latter occurring only rarely. The lamellibranchs are 
represented by species of Inoceramus, Plicatula, and Spondylus, and the 
brachiopods by Rhynchonella cuviert, Terebratula semiglobosa, and Terebra- 
tulina striata. Gastropods are of rare occurrence. Echinoderms are 
represented by the characteristic Holaster subglobosus, and crustaceans by 
Enoploclytia. Examples of these fossils are to be seen in the Luton and 
St. Albans museums. Exposures of the bed are not unfrequent along 
the line of the Chalk escarpment at Totternhoe, Sewell, Puddle Hill 
Sundon, Sharpenhoe, and Barton. 
Overlying the zone of Holaster subglobosus is a soft grey chalk or 
shaly marl known asthe zone of Belemmnitella plena, or to use the most 
modern terminology, Actinocamax plenus. This is remarkably persistent 
across England from the south-west to the north-east coasts. The 
presence of a seam of impure limestone at this horizon indicates a 
marked change in the conditions under which it was deposited, and in 
explanation of its formation the theory has been advanced that a sub- 
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