786 STRATIGRAPHICAL GEOLOGY. [Book VI. 
estuarine sandstones and shales in Yorkshire. These differences help to 
bring before us some of the geographical features of the British area 
during the Jurassic period. 
The Lis consists of three formations, well marked by physical and 
paleontological characters. In the Lower member numerous thin blue 
and brown limestones with partings of dark shale are surmounted by 
similar shales with occasional nodular limestone bands. The Middle 
Lias consists of argillaceous limestones (marlstones) with micaceous 
sands and clays. In its Yorkshire development this subdivision is re- 
markable for containing a bed of earthy carbonate of iron 15 to 20 feet 
thick, which has been extensively worked in the Cleveland district. The © 
Upper division is composed of clays and shales with nodules of lime- 
stone, surmounted by sandy deposits. 
These three formations are further subdivided into zones according to 
distinctive species of Ammonites, as follows: 1! 
The upper sandy beds contain— 
Ammonites of the groups Harpoceras and Lytoceras. Ammonites (Harpo- 
ceras) opalinus, A. radians, A. Thouarsensis, A. insignis. Ammonites 
(Lytoceras) jurensis, A. hircinus = Jurensis bed of Oppel (Wiirtemberg). 
The lower clays contain— 
Ammonites (Harpoceras) bifrons, A. serpentinus, and numbers of the group 
Stephanoceras, as Ammonites (Stephanoceras) communis, A. (S.) anguinus, 
| A. (S.) fibulatus = Posidonomya bed of Oppel (Wiirtemberg). 
Upper Lias. 
a 5. { ee \(Amatthens) spinatus = Spinatus-bed { Wertonbars) 
os 4, * " margaritatus= Margaritatus-bed ss 
=p At vs (Afgoceras) Henleyi ~ = Davei-bed a 
Te De " (Amaltheus) Ibex = Ibex-bed og 
= 1. + (Aigoceras) Jamesoni = Jamesoni-bed “5 
Zone of sige : : 
Fk iT a ae (Arietites) raricostatus = ‘Raricostatus-bed As 
a4 6, > (Amaltheus) oxynotus = Oxynotus-bed ‘ 
al os 5 (Arietites) obtusus = Obtusus- bed ra 
x 4 4. 5, Lurnert = Tuberculatus-bed ay 
&e 13. xe ‘ Bucklandi = Bucklandi-bed is 
(S.] 2. is (Aigoceras) angulatus = Angulatus-bed - 
| i. “i = planorbis = Planorbis-bed - 
\ resting conformably on Avicula contorta beds. 
The organic remains of the Lias comprise leaves and other remains of 
cycads (Palzozamia), conifers (Pinites, Cupressus, Peuce), ferns ( Otopteris, 
Alethopteris, &c.), and reeds (Hquisetites). These fossils serve to indicate 
the general character of the flora, which seems now to have been mainly 
cycadaceous and coniferous, and to have presented a great contrast to the 
lycopodiaceous vegetation of Paleozoic times. The occurrence of land- 
plants dispersedly throughout the English Lias shows also that the strata, 
though chiefly marine, were deposited within such short distance from 
shore, as to receive from time to time leaves, seeds, fruits, twigs, and 
stems from the land. Further evidence in the same direction ig supplied 
by the numerous insect remains, which have been obtained principally 
from the Lower Lias. These were, no doubt, blown off the land and fell 
into shallow water, where they were preserved in the silt on the bottom. 
The Neuropiera are numerous, and include several species of Libellula. 
* See the masterly monograph on Liassic Ammonites by Dr Wright in Paleonto- 
graph. Soc. Memoirs. 
