Paleo-Geological and Geographical Maps of the British Islands. 281 
30° W. may be the modern indications.* The Oolitic beds of Brora—with coal 
—indicate marginal conditions alone the north-eastern coast of Scotland ;+ while, 
as Professor Judd has shown, these beds are well represented in Sutherlandshire, 
and were deposited close to land; so that it is probable the Oolitic sea stretched 
from the north of England round the eastern coast of Scotland, during and after 
the period of the Lower Oolitic. 
It is altogether uncertain whether the Oolitic strata were formed over the 
north of Ireland; but, if so, they had been swept away by denuding agencies 
previous to the Cretaceous period, as no strata of the Jurassic group higher 
than the lower beds of the Lias are found in that country.{ It is probable that the 
whole of the south and west of Ireland were in the condition of land during this time. 
Whether any portion of the central ridge (or “ Backbone,”) of the North of 
England remained unsubmerged during the Oolitic period is uncertain; but that 
the sub-Cretaceous ridge was in part (at least) uncovered by strata of this period, 
may be considered as highly probable, owing to the entire absence of representa- 
tives of the Jurassic period in the borings of Ware, Turnford, and London; On 
the other hand, the sub-Wealden boring near Battle, in Sussex, has shown that, 
to the south of this ridge, the Jurassic sea prevailed, and was deep; as the 
Kimmeridge clay was entered at a depth of 255 feet, and extended down to 
1,769 feet, below which the coralline Oolite was penetrated to a depth of 51 
feet.§ The sea of the south of England stretched southwards into France, and 
probably had its western margin in Devonshire, Cornwall, and Normandy, while 
its northern limits stretched from the Thames valley eastwards, to the south of 
Ostende, where (as already stated), the Lower Silurian rocks are found beneath 
the Cretaceous. 
It will thus be seen that during the period now under consideration, the British 
Isles constituted a group of small islands surrounded by waters which overflowed 
the lower tracts and extended into the Atlantic. On the other hand, part of the 
Atlantic Ocean itself was to some extent in the position of dry land, from which the 
sediment constituting the sands and clays of the Jurassic series were probably derived.| 
* Geikie’s Geol. Map of Scotland. Dr. W. Frazer, of Dublin, has shown a map about 200 years old, 
by Tassin, the Geographer Royal of France, in which “the Sunken Land of Busse,” now only a rock, 
is shown, and which was coasted by one of Frobisher’s ships for three days. As Dr. Frazer has shown, 
the North Atlantic appears to have undergone considerable subsidence in even recent times, of which 
the traditional island of Hy Brasil, off the coast of Ireland, is an illustration. Journ. Roy. Geol. Soc. 
Irel., vol. v. (n. sec.) p. 128. 
~ Murchison, Trans. Geol. Soc., Lond., vol. ii. 2 ser., p-. 393. 
{‘ Phys. Geol. and Geog. of Ireland,” p. 52. 
§ Third Report of the Sub-Wealden Exploration Committee, by Messrs. H. Willett and W. Topley 
(1875), pp. 346-7, 
|| This view I have developed in my paper on “The South-Easterly Attenuation of the Lower 
Secondary Rocks.” Quart. Journ. Geol. Soc., vol. xiv. (1860.) 
TRANS, ROY. DUB. SOC., N.S., VOL. I, 3A 
