206 Mr. llobberds's Replij to Mr. R. C. Taylor. 



at last occupied the space abandoned by the retiring sea. In 

 this stage the superficial bed of alluvial mud began to accu- 

 mulate; aquatic plants took root in it; and it was thickly in- 

 habited by the various races of river moUuscae, that succeeded 

 the testaceous progeny of the ocean. While the surface of 

 this growing mass was slowly raised, that of the waters above 

 it was gradually lowered by the falling level of the basin into 

 which they flowed ; and when by this drain the attrition of the 

 current was brought to work upon the uncompacted body of 

 soft mud, the streams cut out for themselves the channels of 

 the existing rivers. Into these channels the waters settled by 

 degrees ; and as they continued to be drawn off by the depres- 

 sion of the sea, in time they left uncovered the level of the 

 deposit which they had formed. But when in rainy seasons, 

 or after a rapid thaw, they came down more copiously than 

 usual, and in conjunction with this circumstance an extraor- 

 dinary elevation of the tide offered a temporary obstacle to 

 their passage, their outfall being thus stopped, they were 

 turned back in their course, and necessarily rising above their 

 common height, they spread themselves over the face of the 

 new lands. This was undoubtedly the cause of the inunda- 

 tions that were so often experienced here in former times : 

 and on the same principle the yearly overflow of the Nile has 

 been most rationally accounted for, by ascribing it to the joint 

 action of the torrents from the mountains of Abyssinia, and 

 the etesian or periodical winds, the latter of which, blowing at 

 that season invariably from the north, raise the level of the 

 Mediterranean on the coast of Egypt, and for a time check 

 the outflow of the swoln river. In the more consolidated 

 and higher grounds of the Norfolk valleys, such floods have 

 now been for many years entirely unknown ; and in the lower 

 districts they have become less frequent, less extensive, and of 

 shorter duration. Yet while this change has been in progress, 

 greater apparent impediments have been opposed to the de- 

 parture of any superabundant waters, by the acknowledged 

 contraction of the channel of the river, and the accretion of 

 the bar at the mouth of the haven. The increased facility 

 with which they have nevertheless been carried off", and the 

 evident depression of the surface of the river under such cir- 

 cumstances, imply the existence of some latent cause, percep- 

 tible only in its effects, and sufficiently powerful to more than 

 counteract difficulties, from which such opposite consecjuences 

 must otherwise have resulted. That cause cannot be found 

 in the mere unassisted " precipitation from waters charged 

 with alluvial mud;" superadded to this, there must have been 

 a permanent subsidence of the waters themselves, and that 



subsidence 



