1850.] AUSTEN SANDS AND GRAVELS OF FARRINGDON. 469 



conglomerate must be very trifling, as it occupies only a narrow 

 breadth of land in advance of the ridge of gault clay, and is quickly 

 succeeded by the Kimmeridge clay. 



At Rowde, and the other places at which we subsequently saw 

 these beds on our way to Calne, they are evidently thicker ; and in 

 their general arrangement and composition closely resemble the more 

 ferruginous portions of the Farringdon gravel beds, such as those of 

 Fernham. At Stock-Orchard, near Calne, we again saw the ferru- 

 ginous conglomerate resting on the surface of the Kimmeridge clay, 

 and not having any great thickness or continuity, as the Kimmeridge 

 clay had been reached through it, and emerged from beneath it in 

 the south. It is this locality which aiforded what is apparently a 

 rare shell in this deposit — the Biceras Lonsdalei, Sow., figured 

 amongst the illustrations to Dr. Fitton's memoir. 



No one can reasonably doubt the geological identity of the iron- 

 sand and gravels of Devizes, Rowde, and Calne with those of Far- 

 ringdon. The same specific forms of Niicula, Opis, Emarginula, 

 and Terehratula, connect them one with another. 



The ferruginous sands and gravels which we have thus identified 

 as of one and the same geological level, on better evidence than was 

 before possessed, are referred by Mr. Conybeare to his group of ' Iron- 

 sands,' an assemblage of deposits grouped together from the circum- 

 stance of presenting a large proportion of iron, and including the 

 ironsands of the Weald, some of the ferruginous portions of the 

 upper greensand, as well as the deposits here in question. The im- 

 propriety of classing these several masses together was apparent, 

 when the freshwater origin of the ironsands of the Weald became 

 established. 



It will be seen by the sections, as well as from the account of the 

 mode of occurrence of these several masses of ferruginous sands, that 

 the line of the Devizes Canal and its vicinity is the only one along 

 which they occur in an intermediate position between the gault and 

 the Kimmeridge clay ; and it was this circumstance I imagine which 

 induced Mr. Lonsdale to refer them to the cretaceous series, whose 

 views were adopted subsequently by Dr. Fitton. The superposition 

 in this case will be presently considered, whilst the amount of fossil 

 evidence, as exhibited in Dr. Fitton's paper, would hardly admit of 

 the identification of the beds of Rowde and Lockswell Heath with 

 the lower greensand. 



Geologists who may be disposed to take Mr. Lonsdale's and 

 Dr. Fitton's views respecting the cretaceous age of the ferruginous 

 sands and gravels, or, as they had better henceforward be called, the 

 "Farringdon beds," will naturally lay great stress on the De\^zes 

 section : what we have therefore to inquire is, the real value of this 

 particular instance of superposition. It is by no means a necessary 

 consequence, that an arenaceous deposit, because it occurs in an inter- 

 mediate position between the gault and the Kimmeridge clay, should 

 be of the age of the lower greensand : if this sand was the only geo- 

 logical link required to fill up the interval between the two forma- 

 tions, the inference might be allowed ; whereas we know that a vast 



