Parr II. Sxor. ii.§1.] JURASSIC. 173 
has directed attention to the remarkable ternary arrangement of the 
English Jurassic series.’ Argillaceous sediments are there succeeded 
by arenaceous, and these by calcareous, after which the argillaceous 
once more recur. No fewer than five repetitions of this succession 
are to be traced from the top of the Lias to the top of the Port- 
landian. Such an alternation of sediments points to interrupted 
depression of the sea bottom.? It permitted the growth and preser- 
vation of different kinds of marine organisms in succession over the 
same areas,—at one time sand-banks followed by a growth of coral 
reefs, with abundant sea-urchins and shells, and then by an inroad of 
fine mud, which destroyed the coral-reefs, but in which, as it sank to 
the bottom, the abundant cephalopods and other molluscs of the time 
were admirably preserved. 
A characteristic feature of the Jurassic fauna is the abundance 
of its beds or reefs of coral. During the time of the Corallian 
formation in particular the greater part of Europe appears to have 
iif AAS 
Ht aft HEARN 
eS AEH We) Oa ANG TH 
WW HE Fy } 
4 g 
AAG Ye ME LS i J 
RAY ARMA il ] | f 
NM f 
ad 
5 eet AE ce 
A 7 
Lo re ~ 
2 So 
a ws 
[4 ‘ ee 
ix AZ ARO 
WIZZ) SS ale SNE aay 
| WZ Z\NS [ ALN tally i f 
WY i T/G \ ly iA Ny h 
= = Y N VESTA WN vi 4 
ALAS 4 = RaRiel HAIG 2H / nat 
EF SS" ‘in uit F 
44 )}\\\ “WBA = MAL TH pili 
KZ S V4; a\s ip DAY Slnlining 
‘' AS YG BA ie ey! i 
| SW ZH) 1 ‘We it iy Hay 
1) es % ¥ bi hh 
‘en S a 4 
G) HENS ! } 
LOG] i Nh LL = i 
A 
Vv; . j SY) 
SS 
—F Sa 
— 
IEE, 
FEI, BTSs 
LAGE 
S LY se . 
Ley, 
= Ghee a 
yy ds 
ty ie . 
ZZ —— 
= 
,4———— FI \ 
. 
Siu 
GH hy 0H 
HITE BA 
Hl bal | i i 
i a OH ti wl els 
=i Wil 4 od 
\ | Ay 
AN ] Ulf d) 
RAN Wi f Mis 
oA i eye i} 7 h "| 
1 \ i Hill Wij 
\ ARN WT aU A ft} 
i i AWE j i] } 
\ \ Loh f i 
q WY fff y 
Wega 
H If YT 
\ WELD yy, 
iN i} 
Stiff 
Y, 
Wf 
WY 
WY = 
SZ 
La 

a, Isastreea helianthoides (Goldf.); b, Montlivaltia dispar (Phill.); e, Comoseris 
irradians (M. Edvw.). 
been submerged beneath a coral sea. Stretching through England 
from Dorsetshire to Yorkshire, these coral accumulations bave been 
traced across the Continent from Normandy to the Mediterranean, 
and through the east of France and the whole length of the Jura 
Mountains, and along the flank of the Swabian Alps. The corals 
belonged to the genera Isastrea, Thamnastrea, Thecosmilia, Mont- 
livaltia, &c. (Fig. 865). Echinoderms were abundant, particularly 
crinoids of the genera Pentacrinus, Hatracrinus (Fig. 366), and 
Apiocrinus, several forms of star-fishes, and numerous urchins, among 
which the genera Acrosalenia, Cidaris (Fig. 367), Diadema, Echino- 
brissus, Hemipedina, Pseudodiadema, Clypeus, Pygaster, and Pygurus 
were conspicuous. The brachiopods yet found are chiefly species of 
Rhynchonella and Terebratula (Fig. 369); the last of the ancient 
group of Spirifers and of the genus Leptena (Fig. 568) disappear 
in the Lias. Among the lamellibranchs some of the more abun- 
1 Geology of Oxfordshire, &e., p. 393. 2 Ante, p. 498. 
