A HISTORY OF ESSEX 



water in some places for a mile in width ; but my more intimate know- 

 ledge of the upper part is confined to near Mistley, where I have often 

 collected and dredged, though it is too far up to be satisfactory. 



It will thus be seen that though I have fairly well studied some 

 districts there are large tracts which I have never examined, on account 

 of being too far from any convenient anchorage. It must also be borne 

 in mind that my account of the marine invertebrata of Essex has been 

 made much less complete than it would have been owing to difficulties 

 connected with the oyster fisheries. One cannot dredge in some most 

 suitable and convenient places, and in some cannot even use a small light 

 trawl. In some no one is, or was, allowed to collect on the shore at low 

 water, or to dredge even where there are no oysters. If special facilities 

 had not been conceded to me this article could not have been written. 



The total length of the coast, including the chief estuaries and 

 creeks, is considerably over 200 miles, and it would take a long time to 

 examine properly the whole. Some of the animals found are so rare 

 and so local that possibly many more species occur than I have been 

 able to collect, though there may not be so much variation along the 

 exposed coasts as in the estuaries. These play a most important part, 

 since the total length of their shores is fully three times that of the more 

 open coast. In summer the water is not much less salt than in the sea, 

 and in some special cases even more salt. The extremes of temperature 

 are also great, since there is relatively such a large extent of very shallow 

 water and of mud banks left dry when the tide is low. In summer 

 in the Orwell I have known it as high as 74, and in winter some of 

 the estuaries are occasionally filled with masses of ice. The conditions 

 are therefore very unsuitable for certain kinds of animals, and they 

 probably explain why some common species are of smaller size than 

 elsewhere. At the same time there is a tendency for the colder water to 

 sink and pass out to sea, and for the warmer to remain in the estuaries 

 and creeks, and therefore in the long run for these to have a higher 

 temperature than the more open water. This is probably one great 

 reason why some parts of the Essex district are so admirably fitted for 

 oyster culture, since the proper development of spat depends so much on 

 a sufficiently high temperature. 



Along the coast of Essex there are thus no quiet deep water, and no 

 rocks, and no clear rock-pools, but strong currents and great stretches 

 of gravel, sand and mud ; so that the animals found are necessarily of a 

 restricted character. At the same time these circumstances seem favour- 

 able for certain kinds, and some are common which may be very rare in 

 other districts. 



The coast of Essex is thus peculiar, and estuarine conditions must 

 have great influence as compared with the coast of Norfolk. The 

 following table shows the number of species of such groups of animals 

 as seem to have attracted a fair amount of attention in both counties. 

 Those of Norfolk are taken from a proof of a portion of the Victoria 

 History lent to me by Mr. Walter Garstang. This did not include the 



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