A HISTORY OF ESSEX 



The meteorological conditions of a district have a most important 

 influence upon the flora, plants being peculiarly sensitive to drought or 

 excessive moisture in the atmosphere, and also to winds and other 

 atmospheric conditions. 



Perhaps next to climate the geological formations on the surface of 

 the earth have the most potent influence upon the distribution of plants, 

 and botanists can frequently identify a geological formation by plants 

 which occur on its surface. In the county of Essex the distribution of 

 plants is mainly determined by geological conditions. 



All plants are more or less adapted to their environment. Hence 

 in those districts where the field boundaries are constructed of stone 

 certain plants become more or less rare which elsewhere are com- 

 paratively common ; and in counties from which stone is absent those 

 plants which delight in stone walls are rare or absent. Again, if a wood 

 is converted into arable land or pasturage, plants which need the shade 

 and other forms of vegetable life peculiar to woodland country soon 

 disappear. Pasturage, heath land, cultivated land and river banks have 

 each their peculiar inhabitants. 



In order to show clearly the distribution of plants over any area it 

 is necessary to divide it into districts. When possible it is better that 

 these districts should coincide with the geological formation, or when 

 this is impossible with the natural features of the country. Reference 

 to the geological map of Essex will show that the surface geological 

 formations are so scattered that any division of the county coinciding 

 with the geological structure is practically impossible. 



Watson in his Cybele Britannica has subdivided Great Britain into 

 its river beds, and although the distribution of plants does not in all 

 cases coincide with river beds this system has many practical advantages. 

 Professor G. S. Boulger has suggested the adoption of this system for 

 the county of Essex, 1 and has worked out the districts of Essex on that 

 basis ; but I do not think that for practical purposes this arrangement is 

 as convenient in this county as the purely artificial divisions adopted by 

 Gibson. Therefore in the list of Essex flowering plants here given 

 Gibson's divisions have been adhered to. 



As the geology of Essex is fully dealt with elsewhere it is only 

 necessary here to summarize those features of the surface geology of our 

 county which influence the flora. 



Essex occupies a large part of an irregular tract known as the 

 London basin, which has for its foundation the great chalk formation, 

 and the chalk comes to the surface at Purfleet and Grays in south Essex ; 

 at Quendon, Newport, Audley End and Saffron Walden in north Essex ; 

 and at Great Yeldham and Middleton eastwards. 



London clay, which lies upon the chalk, is a very stiff bluish-grey 

 clay, brown on its surface ; it shrinks and cracks in dry weather, but 

 absorbs much water in wet weather. It occupies a large part of the 

 county, and is exposed over considerable areas. 



1 Transactions of the Essex Field Club, ii. 69. 

 34 



