86 THE LOCAL EXTINCTION OF MOLLUSCS. 



of salt in the field is a very different matter, since during dry 

 weather the evaporation of water from the surface causes an 

 upward movement of salt. Consequently, a much heavier rain- 

 fall than I fin. would be required to effect the desired result. 

 But there is no better method than thorough drainage and trust- 

 ing to the rainfall, and results indicate that in about two years' 

 time the salt may be reduced to harmless proportions, if proper 

 advantage is taken of the natural remedy. Foi the eighteen 

 months from December, 1897, to May, 1899, the total rainfall 

 was 26fin., and a second analysis of the soil showed that during 

 this period the salt had been reduced in some cases to one-tenth, 

 and on the average to one-quarter of the amount present in the 

 beginning of 1898. 



After showing the impoverishing effect which the salt has 

 had upon the soil, attention is directed to the consideration of the 

 crops best adapted for flooded land. Wheat, barle}', oats, and 

 mangolds have all given a fair yield in some cases, and in others 

 have completely failed. Ryegrass, of which much was expected, 

 has proved disappointing, in some cases even failing to germi- 

 nate. The only class of crop or weed that was uniformly pro- 

 ductive was the Cruciferous order, kale, rape, mustard, turnips, 

 and the hated charlock, all prospering where other crops failed. 



Very interesting details are given throughout the paper, 



derived from chemical and cultural experiments, and in their 



extended form, Messrs. Dymond and Hughes' researches are of 



considerable importance from a scientific as well as an agricul- 



ral point of view. 



ON THE LOCAL EXTINCTION AND DIFFUSION 

 OF MOLLUSCS IN ESSEX. 



By J. FRENCH. 

 [Read December 12th, 1896-} 



THE object of these remarks is to show that local observation 

 in our districts may be rewarded by obtaining cases of 

 diminution and increase of species of Mollusca in quite recent 

 times, and to show how small are the factors that effect these 

 changes.' 



I [Mr. French began his paper by some general observations of a more or less theoretical 

 character, on the geological history of the Mollusca, and the agencies which may have caused 

 their variation and distribution. These observations are omitted as being hardly suitable for 

 our pages. The Editor has to thank Mr. T. V. Holmes, F.G.S.,and Mr. W. Whitaker, F.R.S., 

 for very kind advice and assistance in preparing the paper for the press A few notes by Mr. 

 olmes are indicated by the initials T. V. H.— Ku.j 



