2 LIAS OF ENGLAND AND WALES : 
Scotland we find remnants of the strata along the borders of tlic 
Moray Firth, near Cromarty, and in Sutherlandihire ; and again 
in Mull and Skye and other of the western islands and adjoining 
tracts of the mainland. In Ireland tnere are representatives of 
the Lower Jurassic rocks near Belfast. 
The Jurassic rocks of Yorkshire form the subject of a separate 
section of this Memoir ; those of Scotland and Ireland -will like- 
wise be described separately, so that the tracts to which attention 
is now directed, include (1) the main outcrop of the English 
Jurassic rocks from the Dorset coast to the low cliffs of Whitton, 
on the southern Humber shore, together with the underground 
extent of the strata ; and (2) the outlying masses that occur in the 
north and west of England and in South Wales. 
The main mass of the Jurassic strata thus traverses the central 
portions of England in a northerly and north-easterly direction. 
Including both Lias and Oolites, this great system is made up of 
many alternations of sand, clay, and limestone, with every inter- 
mediate variety of these materials ; a system whose maximum 
thickness may be estimated at from 4,500 to 5,000 feet. 
Inclined gently towards the east and south-east, and having 
suffered considerable denudation, the harder and more porous beds 
outcrop in escarpments that face westwards or north-westwards, 
and the resultant features are a series of stonebrash hills and clay 
vales. Among the more prominent ridges are the Cotteswolds, 
tlu.t rise in places a little over 1,000 feet, Edge Hill, and "The 
Cliff " which supports the cathedral ot Lincoln. To these physical 
features especial attention will be given in the sequel. 
The Jurassic rocks being based en the red marls and sandstones 
of the Trias, the downward limit of the system was easily recognized 
bv the early geologists; it was marked off by the " lied ground " 
of the vale of Taunton, the Severn valley, and the central plain of 
England. The upward limit of the series was by no means so clearly 
discerned. The dip brings on newer and newer strata in an 
easterly direction, and the Jurassic formations are in some places 
covered conformably by Cretaceous rocks. Nevertheless ovei 
considerable areas the lowest Cretaceous strata are wanting, and 
higher portions of that system stretch irregularly over the worn 
surfaces of the Jurassic rocks, concealing many of their sub- 
divisions. 
How far the Jurassic rocks extend below ground in the south 
and east of Er gland is of course a matter of speculation. The 
highest member of the system appears at the surface in one part 
of Sussex, and other portions of the Oolitic series have been found 
at various depths in the same county, in Kent, and beneath the 
London area. Further references will be made to this subject. 
Progress of knowledge concerning the Jurassic Rocks 
Researches of William Smith. 
That the Jurassic Rocks of England early received a large 
amount of attention is not surprising. The strata furnish our 
