Ixviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



From that point there is a shallowing of the water towards Ireland 

 to 100, 80, and 67 fathoms, and within ten miles of Cape Clear there 

 is still a depth of 54 fathoms. A denudation to such depths is in- 

 conceivable, but a subsidence not only to that but to much greater 

 depths is perfectly conceivable. If, as is probable, the subsidence 

 was gradual, then the action of the waves and of currents, for a short 

 time at least, would come into play, while the water was still compa- 

 ratively shallow, especially if the subsidence was accompanied by 

 earthquakes or other internal forces, causing fissures and otherwise 

 breaking up and loosening the land. Professor Forbes is of opinion, 

 that all the operations which brought about a change of climatal 

 conditions were gradual. He states (p. 401) that "all the changes 

 before, during, and after the glacial epoch appear to have been 

 gradual and not sudden, so that no marked line of demarcation can 

 be drawn between the creatures inhabiting the same element and 

 the same locality during two proximate periods." We may also 

 infer that subsidence was the chief cause of the formation of the 

 English Channel, St. George's Channel, and the German Ocean. 

 At the entrance of the English Channel, there is a depth of from 

 56 to 70 fathoms, and the mid-channel shallows from thence to 

 28 fathoms off Beechy Head. In the distance from Dungeness 

 to Dover, and from Boulogne to Calais, the sea-bottom is very un- 

 even, the depth of water varying from 10 to 30 fathoms. The great 

 inequalities in the sea-bottom, over all the region under review, are 

 of themselves a strong argument in favour of subsidence, for it is infi- 

 nitely more probable that subsidences would be unequal, than that 

 any denuding force would produce such effects. At the south en- 

 trance of St. George's Channel there is a depth of 60 fathoms, and 

 between Waterford and St. David's Head the soundings are from 38 

 to 54' fathoms. Between Dublin and Belfast Lough the soundings 

 from the shore to the mid-channel between Ireland and the Isle of 

 Man are from 20 to 74 fathoms, and opposite the coast of Galloway 

 they deepen to 99 fathoms. In the German Ocean and North Sea 

 the depths are in general not so great ; but here too there are great 

 inequalities, the soundings varying from 9 fathoms, within four miles 

 of the shore, to as much as 76 fathoms in some places, the shallowest 

 parts being over the extensive banks that prevail in that ocean, such 

 as the Long Forties, the Long Bank, the Dogger Bank, and the little 

 Fisher's Bank off the coast of Scotland. Our author's theory twice 

 supposes the upheaval of the sea-bottom into land, viz. that of the 

 Miocene and that of the Glacial sea, and subsidences are equally 

 conceivable. 



The most extensively continuous tertiary deposit with which we 

 are acquainted, is that of pleistocene age on the eastern side of the 

 southern half of the continent of South America, extending more 

 than 1600 miles northward from Tierra del Fuego, and consisting of 

 the great covering of gravel spread over Patagonia, and of the cal- 

 careo-argillaceous deposit that constitutes the soil of the Pampas. 

 Ivluch as we are indebted to M. Alcide d'Orbigny for the great addi- 



