DR. MORISON-NOTES ON THE CHALK EOCK. 
201 
Luton and Chiltern Green stations, just outside our county. Proru 
this section most of the fossils in my collection have been obtained. 
The section is about a quarter of a mile long, and the thickness 
of the principal band of Chalk Rock is between three and four feet. 
In places we can distinctly trace a second much thinner band of 
the rock a few feet above the other. The section is very much 
faulted, there being three large faults besides many smaller ones. 
The down-throw in one case is from ten to twelve feet. 
The Fauna of the Chalk Rock is of a peculiar character; the 
most noteworthy peculiarity being the number and variety of the 
Gasteropoda. The Sponges also are very numerous and varied. 
Opinions differ very much as to the depth of the sea in which 
our Chalk was laid down. Mr. Jukes-Browne believes that the 
soft white chalk was the deposit of a fairly-deep sea, as he calls 
it, some 500 or 600 fathoms in depth ; analogous, in fact, to the 
globigerina-ooze now forming at the bottom of the Atlantic. But 
we know that the Chalk differs from the modem ooze in some very 
important respects. It consists not only of the remains of Forami- 
nifera, but in great part of fragments of the shells of Mollusca, 
Echinodermata, and other marine organisms, and also contains 
those shells entire. The Chalk also contains a much smaller 
amount of silica in proportion to the calcium-carbonate than does 
the modern ooze. Dr. A. Geikie thinks that though the Chalk was 
accumulated in a -sea tolerably free from land-derived sediment, 
tbe evidence shows that the depth of the water in which it was 
deposited did not at all approach that of the abysses in which 
the globigerina ooze is being laid down at the present day; and 
that the organic remains found in the Chalk present rather the 
character of a comparatively shallow-water fauna. But at any rate 
there can be no doubt that the Chalk Rock must have been laid 
down in a comparatively shallow sea; shallow at least as compared 
with the much deeper water in which the greater part of the 
chalk was deposited. The great abundance of Gasteropoda would 
seem to show this, for they are not specially abundant in other 
parts of the Chalk, and we know that they usually inhabit a shallow 
sea at no great distance from land. 
Appended is a list of the fossils in my collection from the Chalk 
Rock in the cutting on the Midland Railway between Luton and 
Chiltern Green, which have been determined for me by Mr. E. T. 
Newton and Mr. Sharman. 
List of Fossils. 
Spongida. 
Ventriculites impressus 
,, radiatus 
,, mammillaris 
,, muricatus 
,, alcyonoides ? 
,, (4 undetermined sps.) 
Camerospongia campanulata 
,, (2 undetermined sps.) 
Cephalites perforata 
,, (2 undetermined sps.) 
Coscinopora infundibuliformis 
Plocoscypbia convoluta 
,, (4 undetermined sps.) 
Polyjerea, sp. 
Guettardia deltata 
,, stellata P 
Placotrema cretaceum 
and 14 undetermined sponges. 
