EXTINCT MAMMALIA IN MARINE AS WELL AS TERRESTRIAL DEPOSITS. 557 



hypotheses, Mr. Strickland supposes, that after those parts of Worcestershire and War- 

 wickshire before described had been long under the sea, an elevation of some hundred 

 feet converted them into dry land, and that a river or chain of lakes then descending 

 from the north-east, re-arranged much of the desiccated gravel of the northern drift, 

 disposing it in thin strata, and imbedding in it the shells of mollusks and the bones of 

 quadrupeds. This river, it is presumed, may have extended as far as Tewkesbury, and 

 there emptied itself into the marine strait, which Mr. Strickland, agreeing with me, be- 

 lieves to have then occupied the lowest portion of the Vale of Worcester. A final eleva- 

 tion of the land to the amount of 60 or 80 feet is presumed to have reduced the Bristol 

 Channel to its present form • and by this rise the fall between Warwickshire and the sea 

 being increased, the Avon is supposed to have acquired a velocity adequate to carve 

 out its bed to the present level, leaving its ancient detritus at heights of from 30 to 40 

 feet above the present stream. Although I at first held an opinion somewhat different, 

 founded upon the apparent higher antiquity of the quadrupeds whose remains are im- 

 bedded in the Avon deposit, I am now convinced that the fluviatile hypothesis suggested 

 by Mr. Strickland (the same as that by which Mr. Lyell accounts for the formation of the 

 " loess" of the Rhine,) explains naturally and simply the relations of the terrestrial and 

 fluviatile deposits of the Avon to the marine gravel. 



Interesting as these conclusions are, it would be wrong to generalize from the facts 

 on which they are based, by supposing that bones of extinct quadrupeds are only to be 

 found in association with terrestrial and fresh-water remains. For although as a neces- 

 sary result of the early configuration of the land, such collocations must have frequently 

 occurred, many of the examples of the so-called diluvial accumulations, doubtless origi- 

 nally washed down by rivers, must, as above stated, have been often drifted far beyond 

 their mouths to form deltas under the sea. In this way only can we satisfactorily account 

 for the presence of the remains of extinct quadrupeds in the gravel of other parts of our 

 island, associated as they often are with marine shells of existing species. 



