1871.] JUDD PTTNPIELD FOBMATION. 223 



insensible gradations, into the variegated clays and sands of the 

 Wealden. The same is described as taking place in the section 

 (now concealed) of the Ridgway Cutting by the Eev. OsmondPisher *. 

 It is true that Professor Forbes pointed out that, if we compare the 

 shells of the Purbeck with those of the "Wealden, we shall find very 

 few species that are common to both. When, however, we consider 

 the fact that the great majority of the MoUusca and Entomostraca 

 which are regarded as typical of the Wealden have been obtained 

 only from the Mgher portions of the series, the fact will be seen to 

 have but little significance. As is well known, the Purbeck (like 

 the Punfield series) includes certain beds which are of a decidedly 

 marine character and contain shells undistinguishable from common 

 Oolitic species, with an Echinoderm {Hemicidaris purbeckensis, 

 Forbes) which, though not occurring in the marine series of this 

 country, is found in the Upper Oolite of the Jura. Not only is the 

 passage of the Portland into the Purbeeks a gradual one in the 

 typical country of these formations, but, as Mr. Godwin-Austen 

 has shown, we find at Swindon Purbeck beds actually alternating 

 with the Portland rocks f. 



As no break has ever been shown to exist in the succession of 

 Wealden beds in the south of England, we are compelled to conclude 

 that they represent the whole of the vast interval between the 

 Upper Oolite and the Upper Neocomian. 



VII. FOEEIGN EatrrVALENTS OF THE PiTNFIELD FORMATION. 



1. " Urgonien" and " Bhodanien" of France, Switzerland, ^r. 

 — ^That the strata known as *' Lower Greensand " in England re- 

 present the " Aptien " or upper division of the great Neocomian 

 system of Continental authors has long been recognized by geolo- 

 gists. The very careful study of the fossils of the different portions 

 of the Neocomian by Pictet, Renevier, and other palaeontologists 

 has established this correlation in the most satisfactory manner. 

 The beds of white limestone, crowded with shells of the order Rudistes 

 (Chama, Anomia, &c.), and with corals, which constitute the "Ur- 

 gonien " of D'Orbigny, and are so widely distributed in Southern 

 Europe, have everywhere been recognized, both on stratigraphical 

 and palaeontological grounds, as constituting the middle portion of 

 the Neocomian system. In the year 1854 M. Renevier, of Lausanne, 

 who has devoted so large a portion of his studies, with the most valu- 

 able results, to the beds of this age, showed that between the " Ap- 

 tien" and "Urgonieu" another series of beds with a distinctive fauna 

 was recognizable, for which he proposed the name of " Rhodanien" J. 

 To this subformation M. Renevier, after a careful personal examina- 

 tion of the strata and their fossils, assigned the " Perna-beds," 

 " Atherfield clay," and " Crackers " of the Isle of Wight, and the 

 well-known '* Couche rouge " of Wassy, in the Department of th© 



* Trans. Cambr. Phil. Soc. Tol. ix. 



t Quart. Journ. Geol. Soc. vol. vi. p. 464 «t seq. 



\ Bull, de la Soc. G60I. de France, 2ine s^r. tome xii, p. 89. 



k2 



