520 Correspondence. 



I miglit have added, and this is the whole secret of Karnes. For 

 rain, in destroying extensive alluviums, cuts them into the ridges 

 and knolls, called " Karnes." Mr. Mackintosh's facts precisely 

 accord with my theory. Whenever the strata are hard the valley is 

 naiTow, and the river runs in a gorge. In the softer strata above 

 the gorge atmospheric decomposition, the erosion of rain, and the 

 river, cut a wide fled valley at the level of the gorge. Though, 

 according to Mr. Mackintosh's theory "■ rivers (apart from deposition 

 during floods) can only produce inequalities .'' And his expression, 

 "a river, when it enters a plain," shovild be "when it has made a 

 plain." The flood-water of the wide flat plain, checked at the gorge, 

 overflows and deposits an alluvium. The bed of the gorge is 

 lowered ; away goes the old alluvium, and a new one is begun at 

 the lower level of the gorge, leaving remains of old alluviums as 

 parallel terraces on the hill sides. This is the solution of Mr. 

 Mackintosh's " Great Denudation puzzle." His ■' river tricks " are 

 very curious indeed. They make Welsh water quite exceptional in 

 its properties. He assures us that Welsh water-falls do not cut 

 their gorges backward. Will he apply his Welsh rule to the gorge 

 of Niagara ? Welsh rivers, " after long-continued heavy rain, run 

 as clear as crystal." He tells us of " a stream flowing very nearly 

 along the summit of a rocky ridge." To say nothing of a river 

 which, as I understand him, has no channel, while " the groimd on 

 each side slopes away from it." He photogTaphs a small valley as 

 "all that the stream has been able to effect." Is nature to have no 

 smaU valleys because she has large ones ? Mr. Searles Wood's 

 " river tricks " are as fantastic as Mr. Mackintosh's. Indeed he 

 asserts — 



Arduis 

 Pronos relabi posse rivos * 



Montibus, et Tiberim reverti. 



He talks of the ''reversal" (!) of the Medway ! The alluvial 

 flats of the Weald rivers inside the gorges of the Chalk downs 

 result from the easy erosion of the Weald clay. Did the nine 

 rivers which now flow from the Weald hill through the Chalk 

 formerly flow {arduis montibus) to the Weald hill? 



Mr. Geikie ("Scenery of Scotland," p. 308) says of Karnes, 

 "notwithstanding all that has been said and written about them, 

 they are as complete a mystery as ever to the geologists of this 

 counti-y." He describes the Kames at Carstairs as the most remark- 

 able that he knows. They are simply the remains of patches of 

 alluvial plains formed by rain and rivers, and in the act of being 

 carried away by the same agents. They have been formed by the 

 Clyde and its affluent, the Mouse-water. The hard rocks which still 

 form the falls of the Clyde at Lanark, and the gorge of the Mouse- 

 water through Cartland Crags between those falls, have formerly 

 sustained the beds of the Clyde and the Mouse-water as high as the 

 Kames are now at Carstairs, and have allowed the formation of 

 enormous patches of alluvial plains. As the gorges at Bonnington, 

 Corra Linn, Stonebyres, and Cartland Crags have been lowered, 



