Migration of the Chiffchaff. 551 



the old Foundation of the first Nest ; but, as if dissatisfied with 

 the production, it did not so much as deposit a single egg in 

 it. — W. H. White. Old Kent Road, Dec. 10. 1834. 



What is the best Method of preventing the Decomposition of 

 the Sheppey Fossils ? — I have observed in two or three Num- 

 bers of your Magazine some queries respecting the best mode 

 of preserving the interesting fossils found in Sheppey and at 

 Folkstone. A method which I believe to be perfectly effec- 

 tual is, to keep them entirely immersed in water. I have some 

 fragments of fossilised wood which have been bottled in water 

 for, I should think, nearly twenty years; and they are as per- 

 fect as on the day they were first put up. They were ob- 

 tained from the London clay, are fossilised by the white iron 

 pyrites, and would unquestionably have long since fallen to 

 pieces if they had been exposed to the action of the atmo- 

 sphere. I would, therefore, suggest to those who have the 

 opportunity of procuring the interesting fruits of the London 

 clay, at the localities alluded to, always to keep them in bottles 

 filled with water. Such a collection would be very valuable, 

 and not quite so expensive as one of succulent fruits preserved 

 in similar vessels, but in spirits of wine. 



The pyrites collected in Sheppey, by exposure to the atmo- 

 sphere, passes gradually to the state of sulphate of iron 

 (copperas). The mass is lixiviated; and the water, thus im- 

 pregnated, being evaporated in proper vessels, the copperas 

 becomes crystallised. — J. S. Henslow. Cambridge, Sept. 2. 

 1836. 



Art. X. Retrospective Criticism. 



Dark-legged Pettychaps, or Chiffchaff {Sylvia loquax Her- 

 bert, Hippoldis of Latham and Montagu, but not of Linnceus 

 and Temminck) : the Migration of this Species partly doubted by 

 Mr. Neville Wood. (p. 485.) — I can safely assert that by far 

 the great majority migrate. In confinement, the erratic im- 

 pulse is very powerful ; and I have known numerous instances 

 of their settling, during the spring and autumn, on the rig- 

 ging of vessels passing the Channel. The few that remain 

 resume their monotonous double note early in the year, usually 

 during fine weather in February, precisely as also happens in 

 confinement; so that there is little chance of the species being 

 then overlooked by ornithologists. I have only twice met 

 with it in early spring, and have generally remarked that the 

 mass of them arrive much later than is commonly stated. A 

 few are mostly heard about the close of March ; but the ma- 



