the Purbeck and Wealden Deposits of England and France, 287 



has been made by it, and that west of Dorsetshire has been 

 submerged, and its inclination (which was eastward towards the 

 shore of the mesozoic basin) reversed, so that the water of the 

 British Channel now deepens as we go westwards. 



The area of Portugal, which during the secondary period up 

 to the cretaceous age was affected by a line of volcanic upheaval 

 running north and south, is, with the exception of the mesozoic 

 deposits accumulated on its western flank, one of metamorphic 

 rocks, these rocks extending through the Spanish province of 

 Galicia to the Atlantic and to the Bay of Biscay. 



This area was, I conceive, during the oolitic period joined to 

 that of the British Isles and under the elevatory influence of that 

 line of volcanic action to which I have before referred as the 

 system of Portugal prolonged into England. The junction was 

 probably severed by the western depression correlative to the 

 upheaval of the Pyrenees, partly during the cretaceous, and 

 partly during the older tertiary epochs. The extent of the cor- 

 relative depression may be inferred from the extent to which the 

 cretaceous and older tertiary sea-bed of the Pyrenees has been 

 elevated by the upheaval of that chain. If we in imagination 

 restore the junction of the metamorphic system of Portugal with 

 Finisterre and the west of England, and eliminate from the pro- 

 blem the western depressions complementary to the tertiary 

 anticlinals of the South-east of England, and the cretaceous and 

 tertiary anticlinals of the Pyrenees, we shall have little difficulty 

 in restoring the areas of the St. George's Channel and of the 

 English Channel west of Dorsetshire as great valleys — the former 

 opening into the latter, and the latter opening into the meso- 

 zoic basin between Dorsetshire and the mouth of the Seine. 

 These great valleys opening thus, and surrounded as they are, 

 chiefly by lower Silurian formations in which limestone is the 

 exception, or by Devonian or Silurian formations in a more or 

 less metamorphic condition, appear, without speculating on the 

 now submerged formations lying between Portugal and the 

 British Isles, to offer the most probable valleys of drainage from 

 whence came the waters which furnished theWealden sediment. 

 Assuming, however, that this was so, we may nevertheless 

 admit that many subordinate valleys of drainage surrounding 

 the basin contributed to furnish the sediment. But the chief 

 mass of the sediment being accumulated in the region where a 

 river emptying itself through this valley would discharge into 

 the basin, points to that as the principal source of the supply. 



In parting with the subject, I cannot refrain from advancing 

 the conjecture that the Jurassic basin of the Charentes, in which 

 such similar phenomena occur as are present in the Jurassic 

 basin of England and France, was governed by geographical 



