54 



THE GEOLOGIST. 



Fossils of the Trias of Aust cliff and 

 the Lias bone-bed at Axmouth. 



In addition to the fossils mentioned above, I bare collected from these 

 " pebble-beds " specimens of the teeth of — 



Saurichtliys apicalis . 

 8. Mougeoti .... 



8. ?..... . 



Hyhodus Minor . 

 Acrodus minimus 



Hi/bodus- pyramid alis . . 1 -c ■-, * , , x . 



d reticulars . . . .) dossils of the Lias. 



Ji. grassiconus. 

 II. ? 



Lepidotus (two or more species in abundance). 



Sphcsrodus ? 



Gyrodus. 



Pycnodus Mantelli. 

 Acrodus. 

 Strophodus ? 

 .Lamna longidens. 

 Notidans. 



and some others. The greater number of these specimens are more 

 or less broken ; yet many of them are by far too perfect and delicate to 

 have been drifted from a distance. I have also, from the same deposits,, 

 casts of about thirty species of small univalve and bivalve shells, which, 

 at present, I have had no opportunity of identifying. 



The "pebble-beds," therefore, appear to offer double evidence in regard 

 to this " old ridge : " firstly, in affording a proof of its existence as a 

 coast-line ; and secondly, in pointing out a time of its partial submergence : 

 with the latter evidence I have now to do. 



A thin stratum of sand, clay, and pebbles (described by Fitton as a 

 " kind of gravel "), occurs at the base of the Lower Greensand, at its junc- 

 tion with the Wealden. Again, the basement-bed of the Gault, as at Bed- 

 cliffe, contains numerous subangular pebbles. In both of these cases the 

 pebbly strata represent a change in the relative level of land and water, 

 sufficiently extensive to have altered the character of the succeeding de- 

 posits ; and thus it seems probable that the " pebble-beds " at the base of 

 the upper division of the Lower Greensand represent a similar disturbance ; 

 the effect of which, I think, may be easily traced. 



No Greensand deposits older than the " upper" or ferruginous division of 

 Fitton are found to the west of a line drawn from Warminster to the Isle 

 of Purbeck, or north of a line passing from Dover, through Bochester, 

 Croydon, Kingsclere (Hants), and then on to ~\\ arminster, or, in other 

 words, north of Godwin-Austen's "old ridge." Greensand deposits, however, 

 corresponding to Fit-ton's upper division, are found greatly to exceed these 

 limits, both on the north and west. It appears, therefore, to be tolerably 

 certain that the " pebble-beds " at the base of the ferruginous division re- 

 present, and are the immediate result of, a period of considerable depres- 

 sion, during which the Lower Greensand ocean extended itself far to the 

 northward, across a portion of the " old ridge," and westward into Devon- 

 shire. By supposing this ridge to have been cut through or partially sub- 

 merged at this period, one difficulty, at least, as regards the " pebbk-beds," 

 will be done away with — viz. that of the occurrence in one stratum of the 

 fossils of several separate formations. For, supposing such a ridge to have 

 existed as a land-surface from a period prior to the deposition of the Lias, 

 every succeeding deposit must have been brought up against it, as has 

 been suggested by Mr. Austen ; and, consequently, an oceanic cm-rent, in 



