180 Retrospective Criticism, 



this subject, in Vol. V. p. 493., and agreeing with that gentle- 

 man, that " there is, perhaps, no question in botany, which, 

 at this moment, it is more desirable to settle on the sure basis 

 of experiment, than the law which limits the variation of 

 species." What botanist has not been sorely perplexed in 

 deciding satisfactorily whether this or that plant is a variety 

 of some other, or a distinct species ? And, I may add, what 

 strange work has been sometimes made by splitting species 

 ad infinitum ! Facts and remarks, apparently the most trifling, 

 often serve to throw light on a difficult question ; and this 

 circumstance I beg to plead as my apology for troubling you 

 and your readers with the present communication. Yours, 

 — B. Coventry ; June 1 4. 



Singular Subsidence in the Chalk, (Vol. V. p. 446.) — 

 Mr. Moggridge of Woodfield has published, in Vol. V. 

 p. 446., a " singular instance of subsidence portrayed" in 

 an " annexed sketch," which he states himself to " have 

 become acquainted with during his late researches in France." 

 His researches in France must indeed be late, and almost as 

 singular as the instance portrayed ; for the plate is copied, 

 and with the slightest possible variation, from the original, in 

 Cuvier and Brongniart's Description Geologique des Environs de 

 Paris, published so early as 1822. The plate in that work 

 is pi. 1. fig. 3. The " explanations" are translated from p. 327. 

 of the text, but incorrectly, as I beg to show. The bed 

 marked c*, in Mr. Moggridge's " sketch," and c in Cuvier's, 

 is not a " calcareous marl, impure, but friable," which is 

 nonsense; but a " marly chalk, that is impure and friable;" 

 the bed d (d), not " chalk, compact and in small fragments, 

 wrapped in yellow clay," but " altered fragmentary chalk, 

 or in small almond-like masses, united or surrounded by 

 yellow clay ; " e (e), not " a stratum of compact marl, ap- 

 proaching chalk, in large masses," but " a bed composed 

 of great masses of marly chalk ;" f(je), not " chalk with its 

 ordinary accompaniment of flints," but "common white chalk, 

 with its beds of kidney-shaped flints." These corrections are 

 positively necessary to the truth of the facts stated ; for, to 

 say nothing of the difference between " calcareous marl" and 

 " marly chalk," or of " compact chalk and fragmentary 

 chalk," or of " compact marl approaching chalk" and 

 " masses of marly chalk," it is quite clear that Mr. Moggridge 

 does not understand the nature of the beds described. The 

 word " ordinaire," by him Englished into " ordinary," in con- 

 nection with the Jlints, instead of being translated common, as 



* The small letter refers to Mr. Moggridge's sketch ; the large letter to 

 M. Cuvier's. 



