Floor of the English Channel. 69 



have been picked up along the shores of Cornwall or Devon, nor from 

 those of Brittany. We should have to suppose a drift of ice from the 

 east bringing stones from !N^ormandy or from Dorset; bnt from these 

 localities we should expect the debris of various Jurassic limestones 

 which do not occur. 



The assemblage of sedimentary rocks indicated by the pebbles is, 

 in fact, just that which would be likely to coexist on the ground : 

 it points to the superposition of Cretaceous deposits on Lias, Trias, 

 and Permian, which is just the actual superposition in Devonshire. 

 I agree therefore with Mr. Worth in regarding these pebbles as relics 

 of formations which extended into the area of the Channel between 

 Cornwall and Brittany, and as evidence on the strength of which we 

 may discuss the probable extension of the several stages which appear 

 to be represented. 



The Selbornian Sands, which are only about 100 feet thick near 

 Sidmouth, may have thinned out in a distance of 70 miles and in the 

 direction of a land- surface ; or they may have passed into soft and 

 easily destroyed sands without cherts or hard calcareous beds. It is 

 quite possible, however, that some of the so-called flints which 

 Mr. Worth describes as the commonest kind of pebble on the Channel 

 floor may really be cherts. This is particularly probable in the case 

 of those which contain grains of quartz and glauconite, as in 62i, 

 which was specially described by Mr. Worth, for such grains are 

 rarely found in the flints of Turonian or Senonian Chalk. 



The Cenomanian of Devonshire is of small thickness (from 3 to 

 18 feet) and consists of quartziferous limestones which indicate 

 a proximity to land, though this land may have been an island on the 

 site of Dartmoor. The persistence of Cenomanian deposits through 

 x^ormandy makes it very likely that they continued for a considerable 

 distance farther west, but only in the form of soft sands, which, 

 however, may have contained cherts. The absence of any pebbles 

 comparable with the hard quartziferous limestones of Devonshire 

 makes it probable that if the Cenomanian did extend into the area in 

 question its deposits were of the French and not the English type. 



That the whole of the Turonian stuge extended into this part of 

 the Channel area is very probable, though it cannot yet be said that 

 the pebbles afford positive evidence of it, because none of them are 

 quite identical with any Turonian chalks in Devon or Dorset. 

 If Ifos. 41, 58, and 12a were really derived from the zone of 

 R. Cuvieri, the assemblage of organisms prevailing at that time in 

 the Turonian sea south of lat. 50 was not quite the same as that 

 living in the area to the north ; for Polyzoa were abundant and 

 Radiolaria were absent or rare, while the reverse was tlie case to the 

 northward. 



The most important and at the same time the most indubitable 

 identification is that of the Chalk Rock, for its discovery proves that 

 at the epoch of its formation the conditions in this southern area 

 were the same as those prevailing throughout the South of England. 

 Incidentally also it makes it nearly certain that the higher part of the 

 Turonian, i.e. the zone of Terehratulina lata, had a similar extension, 

 because the epoch of the planus zone is believed to have been one of 



