48 -Mr. WeL'stei's Reply to Dr. Filton. [Jan. 



the use of this term, applied indiscriminately to all parts of the 

 bed, would lead to much confusion when it came to be used for 

 economical purposes. 



The appellation of the fourth in Dr. Fitton's hst (my upper 

 ferruoiaous sand) is more difficult to agree upon, since various 

 opinions have been ente.'tained respecting it. If my viev/ of the 

 subject be ultimately found to be correct, that is, if this bed be 

 found to agree with the fenii'jinous sand of the west, it would 

 seem right that it should retain its original name ; for to call the 

 Carstone of IMorfolk and the Woburn sand, &c. the true and 

 onljj green sand, would be such a preversion of names 

 that it could not be tolerated : and should the rock immedi- 

 ately under the chalk in the vale of Pewsey really prove, 

 bv a correct examination, to be the same as the UnderclifF 

 and the Reigate stone, what would be the consequence if we 

 adopt Dr. Fitton's nomenclature? The answer is obvious: it 

 also must be called firestone ; that is, the name green sand must 

 be taken from the bed to Vv'hich it originally belonged, to be 

 attached to another which received it only through an oversight. 

 1 do not wish to insist that this has been the case; but at least 

 the contrary has not been shown ; so far, therefore, Dr. Fitton's 

 decision is premature. However, as it has been caUed green 

 sand by some erauient geologists ; and since indeed it contains, 

 in some places, a great ijuantity of the mineral from which this 

 name has been deiived ; 1 have proposed, in a paper lately read 

 before the Geological l^■ociety, to style it the lower green sand, or 

 {to compromise the matter,) as I proposed before, in my paper on 

 Hastings, j'crrngino-green sand ; the Underclitf beii!g called the 

 upper green sand. By this arrangement, a group will be formed, 

 which niav be called (he green sand furniaiiun, consisting of the 

 upper and lower green sands ; and the blue marl between them 

 will be the marl of the green sand. This marl has indeed consi- 

 derable analogies in its fossils with the bed above it, into 

 which it sometimes passes. 



I'he Hastings beds may continue to be described by that name, 

 until more is known ; and the term ft rruginous sand hitherto given 

 to it maybe relinquished, as that has been applied lo the W oburu 

 sands. 



With respect to that part of Dr. Fitton's paper (p. 307 and 383), 

 whei'e he appears to dissent from the opinions that have been 

 stated on the subject of beds being more irregular than has 

 usually been supposed, arising partly from the want ofcontiiuiity 

 in some, and a difference in the structure and consposition of 

 others, I shall only observe, that the subject on which his own 

 paper and the present treats i'urnishes ample proofs, that the 

 ditJiculties of identifying beds have been frequently underrated 

 by geologists, from their not sufficiently attending to these cir- 

 cumstances. At first, in studying ttie secondary beds, the 



