DORSET-SOMERSET DISTRICT. 49 



most part in a brown-coloured rock of very meagre touch, more or less charged 

 with ironshot ova which have a great tendency to fly upon fracture, leaving cavi- 

 ties which give the rock a somewhat carious aspect. This bed has greater resem- 

 blance to the usual Dundry matrix than any f ossiliferous bed with which I am 

 acquainted in Dorsetshire, and its Gasteropoda are in a peculiar condition in many 

 respects. A very characteristic fossil is Pseudomelania coarctata or turris, and 

 this fossil shows the fine spiral lines in many cases to great perfection. This like- 

 wise is almost the only bed known to me in England where the wavy colour bands 

 of Pseudomelania are preserved to any great extent, as in the Normandy beds. 

 The species of Gasteropoda for the most part have strong affinities with those 

 of H x and H 2 , yet with certain differences which deserve to be recorded. 



In order to show the degree of analogy, not to say of similarity, which exists 

 between the remarkable exposure at Oborne and the " Oolithe ferrugineuse " of 

 Normandy, I give an abstract of Eugene Deslongchamps' remarks with reference 

 to its development in the Department of Calvados. 1 He observes that this forma- 

 tion, never more than two metres in thickness, forms the base of what is for him 

 the Inferior Oolite in the greater part of the Department. It is composed of a 

 yellowish or greyish limestone, sometimes more or less siliceous, and contains a 

 quantity of ironshot (ferruginous) Oolites which give it altogether a peculiar 

 aspect. It is besides remarkable for the enormous quantity of Cephalopods, 

 Gasteropods, and Bivalves which it contains. It is possible to distinguish in most 

 cases three beds. 



The lowest of these is a kind of conglomerate or rather nodular bed, which 

 contains remanie fossils from the upper part of the " Marnes Infra-oolithiques," 

 which, as we have already seen, corresponds in the main to the Lower Division 

 of the Inferior Oolite. Hence in Normandy there is a break between the Lower 

 and Upper Division, and this break is still more marked in the greater part of 

 the Dorset District ; since, in most places, only a doubtful fragment of the 

 Humphriesianus-beds intervenes between the Lower Division and the Parhinsoni-zone. 

 It may be a matter of doubt how far the lowest bed of the " Oolithe ferrugineuse " 

 corresponds to the so-called Sauzei-bed of Oborne, except that it seems to contain 

 a considerable mixture of Ammonites (Am. JSoiverbyi amongst the number) and a 

 crowd of Gasteropods, amongst others great Pleurotomarias so characteristic of 

 the true " Oolithe ferrugineuse." 



The second and thickest bed, says M. Deslongchamps, is the true ferruginous 

 Oolite, the hardness of which is usually considerable, and which is pierced by small 

 ironshot Oolites. This formation, the richest of all in fossils, appears to be 

 characterised by Am. Sumphriesianus, which here acquires a great size. We can 

 scarcely fail to recognise in this the main mass of ironshot Oolite at Oborne (H 2 ), 



1 Op. cit. ; p. 105. 

 7 



