Presidential Address—The Geology of Devon. 503 
particular period indicated in the hypothetical map to which I have 
referred. It is a question for separate consideration whether that 
intervening space of land was wholly or only partially submerged 
at a later epoch during the period of extreme depression. For our 
purpose it will be sufficient to have carried the western margin 
of the Chalk Sea beyond the limits of the Cornish peninsula during 
the period of lowest depression, and this I think we may fairly 
claim. I ought to observe that it is not assumed that the Hnglish 
Channel had any existence at that time. Mr. Jukes-Browne regards 
the Channel as a very modern feature in physical geography, but the 
existence or non-existence of the Channel as a mere excavation will 
hardly affect the question of the westward boundary-line of the 
Chalk Sea. 
One more question of Mr. Pengelly with reference to Cretaceous 
geology remains, viz. the age of the Devonshire Greensand. It 
was Fitton, and after him Meyer, who maintained that the Black- 
down Beds were of Lower Cretaceous age, although before their 
time De la Beche had classified them as Upper Greensand, whilst 
Godwin-Austen described them as possibly a sandy condition of 
the Gault. The littoral facies and abundance of Trigonie, having 
considerable resemblance to Lower Greensand species, led Mr. 
MeYer astray. Dr. Barrois and other authors entered the lists, 
and when Mr. Downes read his excellent paper before the Geological 
Society in 1881, the balance of opinion tended to the view that the 
Gault, or most of it, is represented in the Blackdown Beds, and that 
seemed also to have been Mr. Downes’ opinion. If the Ammonites 
in that gentleman’s collection have been correctly determined, there 
would seem to be a mixture of Lower-Gault with Upper-Gault | 
forms; but as the Upper-Gault of the Hast of England is represented 
to a considerable extent in the West by the Upper Greensand, it 
follows that, if we allow most of the Gault to be represented in the 
Blackdown Beds, such a determination carries the Upper Greensand 
with it, so that both De la Beche and Godwin-Austen were right. 
There is not a trace of Lower Greensand, and when we bear in 
mind that the Lower Greensand has already disappeared to the 
eastward, its revival at Blackdown would be an anomaly. But a 
further argument in this direction, which Mr. Downes, aided by Mr. 
Vicary, was the first to indicate, is derived from the fact that the 
nine lowest horizons indentified at Blackdown are missing at 
Haldon. This proves conclusively that the basal rocks of the Upper 
Cretaceous ever occupy a higher horizon as we proceed westwards, 
and, as we have already seen, this has an important bearing on the 
question of the final westward limit of the Chalk Sea. It is quite 
possible also that the missing beds of Chalk were more siliceous 
than their equivalents further eastwardly, and this would still 
further help to account for the flints so numerous in the Channel 
and adjacent shores. 
There are two points in connection with Blackdown which might 
be mentioned: 1st, Mr. Downes read a paper before the Geological 
Society in November, 1884, ‘On the Cretaceous Beds of Black 
