THE SHALLOW AND DEEP WELL WATERS OF ESSEX. 3 1 



beds again yield us samples ; but at Great and Little Braxted, 

 Great and Little Totham, Wickham Bishop, and Tiptree Heath, 

 where the Glacial gravel is raised and exposed so as to be beyond 

 the influence of the Boulder clay, we also obtain water almost 

 destitute of carbonate of lime. Li the Chelmsford and Maldon 

 districts these are the only parishes yielding such waters. In all 

 others, we find that most of the water in the gravel must have 

 percolated through the Boulder clay which, in some places, is far 

 more pervious than is generally supposed. The springs at Writtle, 

 Roxwell, Chignall, and Ford End are at the edge of patches of 

 gravel, most of which is covered with Boulder clay. As this latter 

 contains a considerable amount of chalk, the water, in percolating 

 through, dissolves a certain amount, and its temporary hardness, due 

 to the dissolved carbonate of lime, is increased {vide analyses). I 

 have also given a few analyses of waters obtained from wells sunk 

 through the Boulder clay to the gravels and sand lying between this 

 and the London Clay, and it will be observed that they contain from 

 ten to thirty grains of carbonate of lime per gallon. 



At present, therefore, I have no evidence that there is any 

 difference between " Bagshot " and " Drift " waters, except such 

 as can be accounted for by the influence of the Boulder clay, 

 or the proximity of villages with defective sanitary arrangements. 



In certain localities, I have observed a peculiarity of the Boulder 

 clay water which I find other analysts and medical officers have 

 noted, VIZ., that the water, when freshly drawn, has the odour of 

 rotten eggs. This smell is due to a trace of sulphuretted hydrogen ; 

 but how the gas is produced, and why peculiar to localised areas, I 

 cannot explain. It is very probably formed by the reduction of a 

 sulphate by some peculiar organism, or by dead organic matter, 

 vegetable humus. The general public, however, invariably ascribe 

 the smell to sewage pollution ; but my analyses do not confirm this 

 opinion. The smell very rapidly disappears if the water is left in an 

 open vessel, the gas being oxidized by the exposure to air. 



In other districts, again, we meet with waters containing much 

 sulphate of magnesia. In such cases the water seems to be derived 

 from small beds of sand in the London Clay. On the east of 

 Galleywood Common we recently made a few trial bores, finding 

 water at a depth of about twenty feet ; but it contained so much 

 sulphate of magnesia (Epsom Salts) as to be unfit for any domestic 

 purpose. At Margaretting Tye there is a well (now closed) yielding 



