Colours of the Swiss Rivers. 209 



The Cause of the Colours of the Swiss Rivers. (VII. 438 — 

 443.) — If Mr. Clarke and J. R. have fertile talents for spe- 

 culation, and a great deal of spare time which they wish to 

 employ in a subject not soon to be set at rest, they cannot fix 

 upon a better than the cause of the colours of the Swiss 

 rivers. (VII. 438 — 443.) On my arrival in this country, it 

 was one of the first things which forced itself upon my atten- 

 tion ; and during fourteen summers, and nearly as many win- 

 ters, it has been to me an inexplicable problem (no proof, 

 my friends will say, of its being a difficult one). I have 

 taxed the chemical, optical, and every other sort of know- 

 ledge, of my various acquaintances, some of them of no ordi- 

 nary attainments ; but all their speculations have ended about 

 as satisfactorily as Corporal Trim's story of the King of 

 Bohemia and his seven Castles ; that is, they left off pretty 

 nearly where they began. Nothing is easier than to study 

 any one river that may be chosen, and to form a most plaus- 

 ible theory, which shall leave nothing relating to its colour, 

 &c. &c, unexplained ; but a day's march will be nearly sure to 

 bring you to the banks of another by which every word of your 

 system will be overturned : for example, let theories founded 

 on the Rhone, or the Rhine, be tested by the Orbe. On con- 

 sidering attentively the whole of the article in VII. 438 — 443. T 

 different as the opinions there expressed may be, I should 

 have little hesitation in saying that they are all partly right 

 and partly wrong. — P. J. Brown. Thun, Canton of Berne, 

 Switzerland, June 22. 1835. 



The Species of Fossil Shell described in p. 103 — 105., and 

 illustrated with a Figure, and deemed a Species of Cbnia, is not 

 a Species of Cbnia. — In reference to my communication in 

 p. 103 — 105., I feel it but justice to Mr. Lyell to state that 

 I was prevented showing him the article in question before 

 I sent it to you ; and, since it has been published, I have 

 received a letter from him stating, that, although at the first 

 sight of the fossil, he conceived it to be a Conia, as stated in 

 his note alluded to, he soon afterwards, by accurately inspect- 

 ing it, came to a similar conclusion with Dr. Mantell, that it 

 is either a hippurite, or, in all probability, of the family of the 

 " Rudistes " of Lamarck. — Robert Hudson, Feb. 6. ] 836. 



A Communication from Dr. Mantell on the same Subject. — 

 Mr. Mantell begs to make a few remarks on the communica- 

 tion from Mr. Hudson, inserted in the February number of 

 this Magazine (p. 103 — 105.), relating to a fossil shell from 

 the chalk at Lewes. 



When the specimen was first submitted to Mr. Mantell's 

 inspection, he informed Mr. Hudson, that, in his Geology of 



