TERRACES AND RIVER VALLEYS OF WESTERN EUROPE. 291 



depressions marked on Professor Hull's map are the courses of old 

 rivers. 



Professoa- Hull's tlieoiy involves the supposition that parts 

 now buried 9,000 feet under the sea must have been dry land 

 and must have continued dry land for a very long period indeed, 

 for deep and wide river valleys are not the creation of a day. It 

 indicates the existence of elevated land during long ages, and it 

 would be more convincing if Professor Hull v^^ovild give us 

 geological evidence to show that such loiio--sustained elevation 

 of tbe area concerned occurred before the present depression took 

 place. 



Then another even greater difficulty occui'S to my mind. The 

 difficulty is entirely in reference to the river courses in the great 

 depressions. 



Professor Hull. — Do you mean across the Great Declivity ? 



General McMaiion. — Yes. My difficulty is that our rivers have 

 always been, and are still, bringing down enormous volumes of 

 mud with them, and we know that when this comes in contact 

 with salt water, by a sort of quasi-chemical action the mud is 

 precipitated; and the precipitated mud is carried by the currents 

 that sweep up and down our coasts under the influence of the tides 

 and wind until it finds a resting place in some depression. The 

 difficulty that occurs to my mind is how could river valleys have 

 remained for so long a period and not have been filled up by 

 silt, for the effect generally of silt is to fill up and to level 

 every depi^ession ? Perhaps Professor Hull can remove this 

 difficulty as he has given so much attention to the subject. 



The Author. — I have to express my great pleasure that my 

 friend Professor Etheridge was able to be present this evening, and 

 I am gratified that he indicates his general assent and approval of 

 my views. 



I must say that I am afraid that I have neither time nor oppor- 

 tunity to spend in making large coloured diagram maps of these 

 features. I should be most happy, if any one would undeitake to 

 do so, to give him any assistance in my power ; but it is quite 

 impossible for me to undertake it. 



I think these Admiralty charts are on a sufficiently large scale to 

 show very correctly the sub-oceanic physical features, and with the 

 paper itself will be published these charts taken by a photographic 

 process from the Admiralty charts themselves. 1 think they are 

 pretty good generally, and when anyone reads the paper with the 

 assistance of these maps he will probably have no difficulty in 



