388 W. D. Lang — The Selbornian of Charmouth. 



also know that in the vast majority of cases these are not true 

 mimetic resemblances, as occur in the animal kingdom, but 

 adaptations to common conditions of the environment. Numerous 

 instances might be quoted, but it may serve to mention the fleshy 

 succulent stems of such Xerophytes as Ewphorhia (Euphorbiacese), 

 Cactus (Cactacese), and Stapelia (Asclepiadacese), and the much 

 divided leaves of such hydrophilous plants as the Batrachian 

 Banunculi (Kanunculacese), Myriophyllum (Haloragidaceee), and 

 Hottonia (Primulacese).^ Indeed, it is fully recognised that plants 

 which are highly adapted may, if found fossil, become a fruitful 

 source of error to the pala3obotanist.- 



If, therefore, the theory of homoeomorphy is permissible as 

 a working hypothesis applicable to fossil plants, then we have 

 not only some explanation of the phenomenon " of similarity in 

 general with dissimilarity in details," ^ which is common among 

 such remains, but an indication of the possible diverse origin of such 

 types. At the same time, it is necessary to guard against an undue 

 application of a criterion of small differences, and consequently 

 a large increase to the number of genera and species already 

 recorded. It is necessarj' to remember that such small differences 

 may be really due to the manner of preservation. But where good 

 characters do exist, however much they may be overshadowed by 

 general resemblances, the adoption of the theory of homoeomorphy, 

 even though it may not in all cases be a safe guide, would usually 

 point to separation rather than to identification. 



II. — On a Fossiliferous Bed in the Selbornian of Oharmouth. 



Ey W. D. Lang, B.A., British Museum (Nat. Hist.). 



THE Charmouth district, situated in the south-west corner of 

 Dorsetshire, consists of valleys in the Lias clays, separated 

 by hills which are capped by Upper Cretaceous rocks, resting 

 unconformably upon the Lias. Black Ven is the name of the cliff 

 face bisecting one of these hills, which, lying between Charmouth 

 and Lyme Begis, divides the valleys of the Char and the Lyme 

 stream. Of this cliff, the lower 350 feet consist of Lias clays and 

 limestones. Above this the succession of beds is explained by the 

 following section : — 



Feet. 

 4. SoU and subsoil, consisting chiefly of the weathered 

 remains of the Chert beds in the zone of Fecten asper, 



as well as of higher Cretaceous beds about 20 



Zone of 



Schloenbachia 



rostrata 



(Sowerby). 



Zone of 



„*„?£.* tf, M. Black and dark green loams 20 



3, Yellowish-browu sand (Foxmould) 60-80 



2. TeUow sand containing three layers of indurated nodules 



(Cowstones) 30-50 



interru2)tus 

 (Bruguiere). 



1 For a short account of these biological groups see Henslow, Natural Science, 

 Tol. XV (1899). 

 '^ Seward: " Fossil Plants," vol. i, chapter v. ^ Buckman: ibid., p. 232. 



