in reply to Mr. R. C. Taylor. 205 



necessary part of the regularly progressive change which is 

 here displayed. But neither have they expelled themselves 

 by their deposits, nor have they been of sufficient frequency 

 and duration, to have been the only agents in raising the land 

 of these districts above the ordinary level of their rivers *. 



It is evident that the sea anciently flowed so copiously up 

 the ffistuary, as to exclude from it the animal tribes which 

 live only in fresh waters. I am not appealing, in proof of this, 

 to the marine exuviae on the sides of the hills ; my observa- 

 tions are for the present confined to those which are below 

 the alluvial mud of the valley, where the beds of sand and the 

 fossil spoils which they contain, attest the early and absolute 

 dominion of the sea. How then have its tides been driven 

 out and compelled to yield this part of their empire to the 

 fresh-waters? Not by the increased quantity and force of the 

 latter; and it has been already shown that they could not 

 expel themselves. Here then again, in another stage of the 

 same operation of Nature, no competent and satisfactory cause 

 can be assigned for a visible and unquestionable effect, but 

 the falling level of the sea. Those who deny the intervention 

 of this principle, supply its place by a confused and contra- 

 dictory train of causes ; while by admitting its cooperation, 

 the whole course of events, from first to last, is made clear, 

 intelligible, and consistent. Its influence, in forming the belt 

 of sand which crosses the mouth of the valley, has been al- 

 ready established by facts and inferences which no theory can 

 overcome ; and it is manifest, that the waves which surmount- 

 ed that bank must have flowed up high into the interior of 

 the country. Allowing their level to have been gradually de- 

 clining, while by their successive deposits the sui'face of the 

 lower beds of sand was progressively rising, the combination 

 of these two causes must necessarily have diminished the 

 amount of the tides that made their way into the inner valley, 

 and will account for their having been finally altogether with- 

 drawn. By this process, room was made for the fresh water 

 to descend from the inland fountains; it then first brought 

 down its mud and the spoils of its vegetable and animal tribes 

 to mingle with the sand and shells of the saline floods ; and 



• Sir William Drummond states in his Origincs (vol. ii. p. 18.), thnt the 

 stratum of black earth deposited bv the Nile in the Valley of Ej;ypt, 

 " rarely exceeds two or three feet in depth." This appears to be the whole 

 amount of the mud |)roduced in the course of more than .';5()0 years by the 

 rej^ular annual overflow of that vast and fertilizing stream. Therefore the 

 average increase must have been less than an inch per century. How little 

 then can have been added to the surface of the Norfolk valleys in the 

 space of about 700 years, by the accidental and uncertain inundations to 

 which the\ have been subject ! 



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