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actions, none excited a greater or more deserved interest than 

 those of Mr. Webster. But first generalizations are almost always 

 pushed too far. After being bewildered with the observation of un- 

 connected facts, the first glimmering of general truth is so delightful, 

 that it often leads us beyond the bounds of fair induction. We are then 

 compelled to retrace our steps, and cast about for new phenomena ; 

 and it is only after a succession of trials and adjustments, that the 

 facts we had at first partially misinterpreted are seen at their pro- 

 per level, and with their true bearing upon each other. The broad 

 conclusions of Mr. Webster, in his comparison of the basins of Paris 

 and the Isle of Wight, are however too firmly established to be ever 

 shaken ; and it is only in his estimate of the subordinate groups that 

 his early essays require either revision or correction : and surely it 

 is no reproach to him that he did not foresee the subsequent disco- 

 veries of MM. Cuvier and Brongniart. 



The argile plastique of Paris is now regarded as a mere local lacus- 

 trine deposit. The plastic clay of this country is, on the contrary, an 

 arenaceous formation of enormous thickness, not merely coextensive 

 with, but often stretching far beyond the limits of, our tertiary basins ; 

 and containing, here and there, subordinate argillaceous beds, and 

 many marine shells of the same species with the characteristic fossils 

 of the London clay. 



The deposits of the Isle of Wight above the London clay are sub- 

 divided (in all our published works) into three principal groups, — the 

 upper and the lower composed of calcareous lacustrine marls in diffe- 

 rent states of induration — the middle one of argillaceous marls sup- 

 posed to be exclusively of marine origin. But it has been long known 

 to many of the gentlemen I am now addressing, and to no one better 

 than Mr. Webster — that in Headdon Hill (which gave the types of 

 all his formations above the London clay), the middle argillaceous 

 group contains innumerable freshwater shells, greatly predominating 

 over the marine, and bands of lacustrine marl differing in no respect 

 from that of the upper and lower groups — that in Norton Cliff (about 

 two miles north of Headdon Hill), the three groups are mineralogically 

 well developed without containing a single marine fossil — that at 

 Hampstead Cliff, where the argillaceous marls have four or five times 

 their average thickness, no undoubted marine shells appear on the 

 true parallel of the upper marine formation* — and that in many other 

 parts of the Isle of Wight the three groups admit not either of mine- 

 ralogical or zoological separation from each other; but are composed, 

 from top to bottom, of an indefinite number of alternations of argilla- 

 ceous and calcareous marls, passing at one extremity into soft unc- 

 tuous clay, and at the other into freshwater limestone f. 



* In the highest part of the argillaceous marls of Hampstead Cliff (about 

 two miles east of Yarmouth), there are, however, two species of Corbulee ; 

 but they occur, if I mistake not, far above the parallel of the "upper marine 

 marls" of Headdon Hill. 



f Anomalies, similar to those pointed out above, are stated also to occur 

 in portions of the Paris basin, and may perhaps hereafter be used as terms 

 of comparison with the structure of the Isle of Wight. 



