A HISTORY OF BEDFORDSHIRE 
the existing outlines of the hills overlooking the valley of the Lea in 
South Bedfordshire. The most instructive exposure is that on the Mid- 
land Railway between the 284 and 284 mile marks. At the deepest 
part of the cutting the following beds are seen in descending order :— 
The base of the Upper Chalk with numerous flints, about 20 feet ; 
upper seam of Chalk Rock, 2 feet; white chalk with few flints (the 
Micraster-bed), 10 feet; lower seam of Chalk Rock, 2 feet; Middle 
Chalk with few flints, 30 feet. The beds are approximately parallel 
and are interrupted with occasional faults, the dislocations being very 
apparent in the seams of Chalk Rock. 
The series of beds thus shown indicates several variations in the 
depth of the sea which were accompanied by changes in the fauna. 
That for the Middle Chalk below the Chalk Rock suggests a deep sea 
of 1,000 fathoms or more; that for the lower bed of Chalk Rock 
much shallower water ; again a deepening for the Micraster-bed, followed 
by another period of shallower water during the formation of the upper 
bed of Chalk Rock ; and then a great depression of the sea-floor during 
the deposition of the Upper Chalk. 
Much original work on the paleontology of the Chalk Rock has 
been accomplished in recent years, especially by Dr. Morison* and Mr. 
Henry Woods,” the latter of whom has figured and described several 
species found near Luton. ‘The most prevalent forms which occur in 
this district are the sponges Ventriculites, Cephalites, and Plocoscyphia; the 
echinoderms Micraster, Holaster, and Echinocorys; the gastropods Trochus, 
Turbo, Avellana, Aporrhatis, and Pleurotomaria; and the cephalopods 
Nautilus, Ammonites, Scaphites, Turrilites, Baculites, Ptychoceras, and Hetero- 
ceras. ‘Taken in the aggregate these genera present a group which is 
incomparable with any other in the Chalk series. 
The absence of flints in the Chalk Rock, and the finding of a pebble 
of quartzite in it near Luton, are noteworthy. 
The deepening of the sea at the commencement of the Senonian 
or Upper Chalk period was accompanied in this area by a great paleon- 
tological break which indicates a cessation of deposition of strata for a 
prolonged interval after the formation of the Chalk Rock. The presence 
of dislocations in the lines of bedding in the Middle Chalk and their 
absence in the Upper Chalk are confirmatory of the assumption that 
there were great oscillations in the level of the sea-floor at the close of 
the Middle Chalk period. The surface of the Chalk Rock also some- 
times appears to show indications of erosion. 
The Uprer Cuatk, of which only the lower portion is present in 
Bedfordshire, covers the summits of the hills in the south of the county, 
and is often concealed by accumulations of gravel, loam, and clay. 
That it has been subjected to an enormous amount of denudation is 
attested by the numerous flints which are present in the superficial 
deposits of the district. Those in the drift gravels are usually much 
1 «Notes on the Chalk Rock,’ Trans. Herts Nat. Hist. Soc. v. 199-202 (1889). 
2 ¢The Mollusca of the Chalk Rock,’ Quart. Fourn. Geol. Soc. Iti. 69-98, liii. 377-404 (1896-7). 
22 
