124 PROCEEDINGS OP THE GEOLOGICAL SOCIETT. 



bankment to the west of that point for some distance, it is difficult to 

 place Mr. Prestwich's section at any other point than where I sup- 

 posed it was taken, on account of the configuration of the ground. 

 "WTiether there was chalk, or not, at any one point, is quite imma- 

 terial to my argument. I do not find the Montiers section at all as 

 represented by Mr. Prestwich and Sir C. Lyell. (See fig. 12, p. 123.) 



The Montiers section appears to be the one adopted as a type of 

 the Somme district, first by Mr. Prestwich and afterwards by 

 Sir C. Lyell. Both authors represent, in several sections of the 

 Somme, a great extent of chalk, separating highly inclined beds of 

 gravel, which they have distinguished in age by its position above 

 or below this outcrop of chalk, as upper- and lower-, or high- and 

 low-level gravels. The sections which I place before the Society 

 appear to me, on the contrary, to show that this distinction is not 

 a real one, but that the deposit of gravel is one and continuous, de- 

 posited in concavities of an ancient chalk valley, and is not highly 

 inclined as represented in the ' Antiquity of Man ' and the ' Philoso- 

 phical Transactions.' 



In page 264, Phil. Trans. 1864, Mr. Prestwich gives a theoreti- 

 cal account of the view he takes of the deposition of the gravels. 

 Part of the upper-level gravels are represented as remaining un- 

 touched, while the vaUey is cut down 50 feet, and a newer set of 

 gravels deposited at lower levels ; my sections show that there is 

 no evidence of any such action. 



The same views are extended by Mr. Prestwich to the loess 

 deposits ; the loess of St. Acheul is considered a much older depo- 

 sit than the loess at Montiers. 



Mr. Prestwich lays great stress, in his paper in the Society's 

 Journal, p. 500, on the valley being too large to admit of the 

 possibility of its being filled with water up to a height of 100 feet 

 above the present water-level. 



I have already submitted the argument that we ought to judge 

 of the height of a flood by means of the debris it has left, and not 

 by any theoretical notions of our own. 



In 1866, twenty inches of rain feU in Scinde in twenty-four 

 hours, in a flat country intersected by rivers. Mne girders, weighing 

 nearly eighty tons each, were washed off the piers by the Mulleer Eiver 

 from the Pailway JBridge, situated sixteen miles above Kurrachee 

 (fig. 13). This bridge consisted of eighteen girders (see Plate IV. 

 fig. 10.) They were not box girders, but made of wrought ii^on on 

 Warren's system. The bottoms of these girders were sixty-five feet 

 above high-water mark, spring tides, Kurrachee Harbour, and se- 

 venty-four feet above low- water spring tides. They fell in the 

 course of six hours ; and one girder of the weight of eighty tons was 

 carried two miles down the river, and nearly buried in sand*. The 

 section of the river bridge is represented (Plate IV. fig. 10). The fall 

 of the Mulleer Eiver only averaged ten feet per mile for fifteen miles 



* Mr. John Brunton, F.G.S., Chief Engineer of the Scinde Eailwaj, was pre- 

 sent at the Meeting, and confirmed this statement, which he had previously 

 given me. 



