THE SHALLOW AND DEEP WELL WATERS OF ESSEX. 35 



The East Donyland water contains about fifteen grains of carbonate 

 of soda per gallon, the Colchester water No. I. about six grains, and 

 No. II. none, the whole alkalinity being accounted for by the 

 lime salts present. In all respects the Donyland water closely 

 resembles many of the sand waters. Amongst this group of moder- 

 ately soft waters we find the amount of chlorides varies very 

 considerably ; but the wells yielding the largest quantity are sunk 

 near the sea and close to a tidal river, the Blackwater. It will be 

 observed that the waters in these two groups are all obtained from 

 wells at and south of Colchester. North of that town all the deep 

 well waters I have examined are from the chalk and contain over 

 ten grains of carbonate of lime per gallon. They therefore fall into 

 group III. (Table V.). 



The first eleven waters in this group, and five out of the last six, 

 are derived from near the outcrop of the chalk or from places in 

 which the London Clay and Tertiary sands are thinning out. In 

 nearly all, the chlorides are very small in amount. The exceptions 

 are at Mistley and Grays, both near the sea or a tidal river. In nearly 

 all the alkalinity is due to carbonate of lime, the exceptions being the 

 Mistley water, which contains probably about four grains of carbonate 

 of soda per gallon, and the Stratford water (Phoenix Works), which 

 contains about ten grains. The only other sample from Stratford 

 (Howard's Chemical Works), on the other hand, contains little, if any 

 carbonate of soda. Many of the Tertiary sand waters are very hard 

 (due to both magnesia and lime), but contain very much more 

 chlorides, sulphates, etc. (of soda chiefly), and some are so brackish 

 as almost certainly to suggest infiltration of sea water. This is more 

 probable, since all of them come from sources near tidal rivers or the 

 sea. The last water on this list, that from the Beckton Gas Works, 

 resembles some of these waters in being brackish ; yet it is sunk well 

 into the chalk, and I am told that many wells in that neighbourhood 

 have been sunk to considerable depths into the chalk, yet have 

 yielded waters so brackish as to be useless, and the wells have been 

 closed. 



Reviewing the whole three groups, we find that most of the chalk 

 waters in the south of the county and in the north-east resemble 

 each other in containing considerable amounts of carbonate of lime 

 and very little chloride and carbonate of sodium ; but differ from the 

 chalk waters in other portions of the county, where the chalk lies 

 St a much greater depth, since the latter contain very little lime and 



P 3 



