Dr. Fitto)i's Additional Remarks. 461 



plex, will make it evident that a great deal is still to be deter- 

 mined respecting the beds below the chalk in those districts. — 

 And since it is probable that a greater consistency of structure 

 than has hitherto been suspected will be found to pervade the 

 whole of the extensive tract now mentioned, even this rapid 

 view of what remains to be done, will show how much there is 

 to reward inquiry in this department of the geology of England. 



It has been suggested to me, from different quarters, that the 

 terms upper and loxver greensand would be preferable, for the 

 denomination of the beds which I have named firestone and 

 greensand ; and that these two strata, together with the inter- 

 vening gault, might form one group, in the general arrangement, 

 under the name of "the greensand formation." But the mis- 

 application of the term greensand has really been the source of 

 so much confusion, that it seems much better to give it up alto- 

 gether, and to choose for the beds in question names entirely 

 new. — I know indeed that some of the principal geologists in 

 England concur in this opinion. And the propriety of group- 

 ing together the firestone and greensand is also doubt- 

 ful : — because the firestone beds are not in general separated 

 from the chalk by any well marked natural feature, but pass 

 into the lower part of it almost insensibly. They sometimes, it 

 is true, project beyond the foot of the chalk escarpments so as 

 to form a sort of step or lower plateau, as at St. Catherine's 

 Down in the Isle of Wight ; — but there never is between the two 

 strata a well defined valley, such as that which contains the 

 gault, and separates the firestone from the greensand, — a 

 natural and characteristic feature that is seldom wanting. It 

 may be added in support of this objection, that the French 

 naturalists consider the firestone as a variety of the chalk itself, 

 and have named it accordingly craie-tufau, glauconie~cra- 

 yeuse, &.c. 



I have employed the term firestone to designate the beds 

 above ailuded to, merely for the purpose of distinction ; but it 

 is, perhaps, objectionable, inasmuch as the true firestone forms 

 a part only of the beds to which the name of the stratum is 

 intended to refer, and is probably not coextensive with the 

 stratum itself. — The principles of geological nomenclature seem 

 to require, that significant terms derived from external characters 

 should be avoided ; since, from the great diversity of composi- 

 tion and appearance which exists in the same stratum in different 

 districts, such terms are very seldom correctly applicable to 

 any great extent : — Of this the greensands, as they have been 

 hitherto denominated, afford a remarkable proof. — The best 

 names, therefore, at present in use, are either those (like gault 

 and lius), which are insignificant themselves, but locally em- 

 ployed, in districts where the strata with which they are con- 



