284 
ELEMENTS OF GEOLOGY. 
the white chalk below. The latter is distinguished by reg¬ 
ular layers of black flint in nodules, and by several shells, 
such as Terebratula carnea (see Fig. 246, p. 294), wholly want¬ 
ing in beds higher than the green band. Some of the or¬ 
ganic remains, however, for which St. Peter’s Mount is cele- 
*brated, occur both above and below that parting layer, and, 
among others, the great marine reptile called Mosasaurus 
(see Fig. 227), a saurian supposed to have been 24 feet in 
length, of which the entire skull and a great part of the skel¬ 
eton have been found. Such remains are chiefly met with 
in the soft freestone, the principal member of the Maestricht 
beds. Among the fossils common to the Maestricht and 
white chalk may be instanced the echinodern. Fig. 228. 
I saw proofs of the previous denudation of the white chalk 
exhibited in the lower bed of the 
Maestricht formation in Belgium, 
about 30 miles S.W. of Maestricht, 
at the village of Jendrain, where the 
base of the newer deposit consisted 
chiefly of a layer of well-rolled, black 
chalk-flint pebbles, in the midst of 
which perfect specimens of Theci- 
deapapillata and Belemhitella miicro- 
nata are imbedded. To a geologist 
accustomed in England to regard 
rolled pebbles of chalk-flint as a com¬ 
mon and distinctive feature of tertiary beds of different ages, 
it is a new and surprising phenomenon to behold strata made 
up of such materials, and yet to feel no doubt that they were 
Ileviipneustes radiatw^, Ag. 
Spatangus radiatus, Lam. 
Chalk of Maestricht and white 
chalk. 
