306 E. E. Soicorth—A Great Pod-Glacial Flood. 



its flow rapid, it acts as a scouring agent, carving out a deeper and 

 deeper channel. Where its fall is slight and its flow gentle, if it be 

 in any way charged with solid materials, it performs the opposite 

 part, namely, it deposits material in its own channel, and tends to 

 raise it. In both cases the great mass of the prodticts of denudation 

 are no doubt carried seawards and deposited as a delta or otherwise ; 

 but in regard to a certain proportion, this is not so. The Rhine is 

 a very good example of what we mean. In its upper reaches, and 

 again in the defiles of the Seven mountains, where it is "throttled," 

 to use an expressive Lancashire word, its rapid and boisterous course 

 no doubt makes it a more or less potent denuding instrument. 

 Above and below the defile just named, where its course is slow 

 and its fall slight, it is constantly raising its own bed, and forming 

 a kind of natural aqueduct. The consequence is that presently 

 its flow is in places above the level of the surrounding country, and 

 has to be carefully banked and dyked, and that it has at various 

 times broken loose and found itself a fresh channel in the wide 

 valley, a process which has been often repeated. The fact is 

 familiar enough in the case of the Lower Rhine, and a graphic 

 picture of its effects in the upper waters of the river may be 

 seen in Reclus's volume on the Geography of Central Europe, 

 recently published, Map 139. The same thing is familiar also in 

 the case of the Lower Thames and Trent. All this is elementarj^ 

 enough, but the corollary which naturally follows from it is not so 

 generally accepted, or rather is too often ignored. A river cannot 

 possibly do both hinds of loorlc at the same time upon the same part 

 of its channel. It cannot at the same time act as a scouring agent 

 and as a depositing one. The two kinds of work are absolutely 

 antagonistic, and we may certainly lay it down as an Inductive Law 

 that periods of destruction and periods of deposition cannot be con- 

 temporaneous in the same river-bed. This law seems to be very 

 much overlooked in some of the current theories about the origin 

 of river valleys. Professor Ramsay, in a well-known paper on the 

 Physical History of the Valley of the Rhine (Journ. Geol. Soc. vol. 

 XXX. p. 81, etc.), says, "There is good reason for the belief that the 

 whole of that part of Germany which is noio the valley of the Rhine 

 betw^een Basel and Mainz was once filled with Miocene strata, the 

 precise thickness of which is to me unknown." He then goes on 

 to argue that a thickness of from 300 to 500 feet, and probably 

 more, has been removed by denudation. When these strata were 

 deposited, he urges, the drainage of the country was not, as now, 

 from south to north, but the other way, and the level of the whole 

 country was very much lower. He then argues that a great disloca- 

 tion took place, causing the upheaval of large tracts in the Alpine 

 district, by which the whole drainage was remodelled. It was at 

 this juncture that the Rhine as a river commenced, on Professor 

 Ramsay's view, its history. "The upper valley of the Rhine," he 

 says, " was at that time filled by a river of ice which, joined with 

 others, covered the valley more than half-way from Schaffhausen to 

 Basel, while from its western edge and end the liquid river followed 



