1856.] WRIGHT UPPER LIAS SANDS. 313 



with, other species enumerated in the list of Conchifera from the 

 Frocester district, and which are found in the limestones and sands 

 of the Inferior Oolite, still it contains a suite of Cephalopoda which 

 are only found in the Upper Lias, and characterize that formation in 

 Germany, France, Belgium, and England : these are — 



Ammonites opalinus, Rein. Ammonites hircinus, Schloth. 



insignis, Schubler. Jurensis, Zieten. 



variabilis, d'Orb. Nautilus inornatus, -Sow. 



discoides, Zieten. Belemnites breviformis, Voltz, 



I 



striatulus. Sow. compressus, Voltz. 



radians, Schlotheim. Nodotianus, d'Orb. 



Raquinianus, d'Orb. irregularis, Schloth. 



With these facts before us, I submit that the amount of palaeon- 

 tological evidence is in favour of our grouping the Cephalopoda-bed 

 and its underlying saads with the Upper Lias, rather than with the 

 Inferior Oolite, to which latter it has been considered to belong, and 

 as the basement-bed of which it has been described. 



In estimating the value of palseontological evidence, we ought to 

 look at its weight as well as its amount. It is well known, for example, 

 that many species of Conchifera and Gasteropoda have a much more 

 extensive stratigraphical range than other Mollusca ; thus, certain 

 forms of these classes have lived in the seas that deposited the Infe- 

 rior Oolite, as well as in those of the Oxford Clay and Coralline Oolite : 

 of which, Trigonia co&tata^ Pecten lens, Myacites abductus, Ostrea 

 Marsha, Myacites Jurassi, and Phasianella striata are examples. 

 But when we inquire what species of Ammonites, Brachiopoda, or 

 Echinodermata are common to the Inferior Oolite and Coral-rag, the 

 answer is none. These three classes are therefore of more value to 

 the palaeontologist than the Conchifera and Gasteropoda, seeing that 

 their species have a more limited distribution in time. 



Ammonites are in fact probably the best indicators of geological 

 horizons ; and this is the more remarkable, seeing that their Cepha- 

 lopodous occupants lived in these fragile shells in the high seas, at a 

 considerable distance from the shore. We know that the Lower, 

 Middle, and Upper Lias contain species which characterize these 

 divisions of that formation in the most satisfactory manner ; and that 

 even the different beds of these three divisions contain species pecu- 

 liar to each. The species of Ammonites found in the lower ragstones 

 of the Inferior Oolite are distinct from those of its upper beds. 

 The same reasoning holds true when applied to the Ammonites of 

 the middle and upper divisions of the Oolitic rocks, as well as those 

 found in the different stages of the Cretaceous group. 



Brachiopoda are likewise good stratigraphical indicators, as has 

 been most clearly shown by Mr. Davidson in his magnificent ' Mo- 

 nograph on the British Brachiopoda.' 



Echinodermata, although lower in the animal series in a zoological 

 point of view, afford the palaeontologist the largest amount of data 

 on which to reason. The Silurian, Devonian, and Carboniferous 

 rocks are all characterized by distinct forms of Crinoidea, most of 



