42 [March 27, 



level gravel is constant, but the high-level gravels are only occa- 

 sionally preserved. Sections are then given to explain the cause of 

 their absence such as where the valley C being wider than the ori- 

 ginal bed of the old river which deposited the gravel d, the latter has 

 been necessarily altogether removed. 



That the formation of the higher gravels can be owing to the 

 action of the present rivers is clearly impossible under existing con- 

 ditions ; for not only are they far above the level reached by the 

 rivers at the highest floods, but also the sectional area of the valleys, 

 compared to that of the present rivers, is so vast, that in no possible 

 way, except by the sea, could they now be filled with water. Sec- 

 tions are given of the valleys of the Waveney, Ouse, Somme, and 

 Seine, showing a disproportion between the rivers at their highest 

 floods and the old valleys, on the average, about 1 : 500 ; and it is 

 shown, with respect to the great flood of the Seine in 1658, when the 

 waters at Paris rose to a height of 29 feet, that it would require a 

 flood of at least one hundred times that magnitude to fill (with the 

 water even in a state of rest) the valley of the Seine to the level of 

 the high-level gravels of Gentilly and Charonne. 



That the isolated beds of high-level gravels must at one time have 

 been connected in length and breadth is evident. from the circum- 

 stance of these detached parts having certain characters in common, 

 and from the fact that if the deep valleys which they overhang, and 

 the transverse valleys which they pass over, had then existed, they 

 would have presented insuperable barriers to the deposition of the 

 gravels at levels so much higher. 



That the transport of this drift could have been caused by the 

 bursting of lakes, by the sudden melting of the glaciers and snow of 

 mountain-chains, or by the transient passage of a body of water over 

 the land is not possible, because the spread of the de'bris would have 

 been more general, would have held its course more irrespective of 

 the existing watersheds, and would have shown an amount of wear 

 in proportion to the distance travelled ; whereas in each basin the 

 debris is local, however low the watershed. None of the slate and' 

 oolitic debris of the Oise valley traverses into the valley of the 

 Somme, notwithstanding the watershed between them is only six 

 miles broad and eighty feet high. 



There are two ways in which the author conceives the spread of 



