SALT MAESHES-PAST AND FUTURE 



ous interpretation of marsh deposits, the case 

 of a similar seashore region, that of the North 

 River valley at Scituate is instructive. Here 

 for many years prior to 1898 the mouth of 

 the river bed had been so silted up that the 

 tides were practically excluded — and the 

 level of the marsh, which supported a fresh 

 water vegetation, came to be, as subsidence 

 continued, several feet below the level of high 

 tide on the outer beach. In the great Novem- 

 ber storm of 1898 the sea broke through the 

 barrier beach some distance from the mouth 

 of the river, and since then the tide has ebbed 

 and flowed freely in the valley, drowning out 

 the fresh water vegetation and killing grass, 

 bushes and trees. The marsh of a salt water 

 formation is gradually building up to the high 

 tide level. Suppose, then, that in the course 

 of centuries this new mouth should become 

 silted up, the influx of salt water excluded 

 as before, the marsh would again take on a 

 fresh water character. If these changes were 

 repeated several times a section would show 

 alternations of fresh and salt water deposits. 

 The unwary geologist might infer, and his 

 inference would be extremely plausible, that 

 there had been times of alternate elevation 



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