of tin Sea off the Coast of British Guiana. 45 



meter been used for ascertaining the specific gravity of the 

 water, where the proximity of the river has been conjectur- 

 ed and laboriously sought for, the enterprising navigators 

 would have had a great aid in solving the problem. It may 

 be said, that the coast of British Guiana is almost peculiar, on 

 account of the many and large rivers by which it is broken. 

 This is true ; and, the diminution of the specific gravity 

 of the water of the sea there is, in proportion, remarkable. 

 Where fewer and smaller rivers have their outlet, there a less 

 diminution, but some diminution, may be expected to be found 

 on approaching land, appreciable by the hydrometer and an 

 indication of the circumstance, — the difference being only in 

 degree. 



In conclusion, I may remark, that the sea for many miles 

 oft' the coast of British Guiana is more or less discoloured ; 

 near the land it is the colour of the Thames at London bridge, 

 — light brown. This, with increasing distance from the shore, 

 acquires a greenish hue ; the pure blue of the ocean is hard- 

 ly observable within eighty miles of the land. In all the 

 specimens of sea-water which I had taken up, with the ex- 

 ceptions of Nos. 8 and 9, there was, on rest, a minute sedi- 

 ment (the cause chiefly of the discoloration), diminishing 

 with the distance at which each was collected. Observed under 

 the microscope, this sediment, in each instance, appeared to 

 consist of granular matter, the granules commonly less than 

 •foJoo iiich in diametei*, and of minute lamiiisB of irregular 

 form, seldom exceeding juVer inch in diameter. The exceeding- 

 firmness of tliis discolouring matter is not surprising, when 

 it is considered that the rivers which are the carriers of it, 

 flow for many miles with a very sluggish course ; and that 

 the bottoms of many of them, perhaps of all of them, in part, 

 are actually below the level of the sea. The discolouring 

 material is, no doubt, chiefly earthy matter, and probably 

 mixed with very minute portions of vegetable and animal 

 matter : this seems to be indicated by the granules being 

 collected together in little masses. Resting on the sediment 

 in the specimen of water taken up close to the shore, was a 

 mucor-like substance. And, it may be, that to the presence 

 of a portion of animal and vegetable matter, the alluvial soil 



