272 J- F. BLAKE AND W. H. UUDLESTON OX 



itself. The following may be deemed an average development of 

 this upper series between the cliffs west of Osmington and its final 

 disappearance in the dip in Ringstead Bay : — 



Kinmieridge Clay. ft- in. 



a. Bed charged with Exogyra nana and many other fossils 8 



b. Blue clays of variable thickness, having usually a large 



quantity of Bhynchonella inconstans towards the middle, 

 with many Serpidce and fossils of a decidedly Kimmerid- 

 gian character say 4 



Upper Corallian. 



1. An Upper Coral Rag, chiefly made up of Thamnastrcea con- 



cinna and Thecosmilia, with an assemblage of highly 

 characteristic fossils, Pecten vimineus, Lima rigida, L. pec- 

 tiniformis, spines of Cid. florigemma &c, in a hard 

 marly grit 8 



2. Thin clay, with Serpula 4 



3. Bands of hard yellow ferruginous clay 1 4 



capping 



4. A waxy unfossiliferous clay, with occasional ferruginous 



corals 9 



5. Red grit (top of the Sandsfoot grits), with Pecten midas, 



Goniomya v-scripta, Ammonites decipiens 5 



6. Ferruginous sandy shale, being a continuation downwards 



of no. 5 14 



7. Sands and shales, with two strong bands of Ostrea deltoidea, 



based upon an intermittent band of shelly ferruginous stone, 



full of small Ostrece and Cardia. Bel. nitidus common... 7 



8. Unfossiliferous shales (the Sandsfoot Clay) 18 



55 4 



The beds vary much both in character and thickness within short 

 distances. Thus No. 1 is not always to be made out west of Os- 

 mington, but is well seen in Ringstead Bay. In the analogous 

 position at Sandsfoot there is a slight indication of this bed ; but 

 nowhere else in the Weymouth district is there such a satisfactory 

 exhibition of Coral Rag as on this horizon in Ringstead Bay — a fact 

 which seems to have escaped the notice of Waagen. Besides the 

 fossils above mentioned, Astarte ovata (peculiar form), Opis coral- 

 Una, and a very large Modiola are characteristic ; there is also an 

 abundance of deltoid oysters both above and below. The Ammonite 

 accompanying this group is a modification of the form figured by 

 D'Orbigny as A. cymodoce, described as a Corallian species. 



A very similar form occurs in the MhyncJionella-bed, which we, 

 in common with Waagen, consider to be the true base of the Kim- 

 rneridge Clay in this locality. . This circumstance would indicate that 

 no very great lapse of time intervened between the two groups. 

 The continuity of deposit is practically unshaken, the character 

 only is changed. But here on this horizon the Corallian fauna 

 apparently made its last stand before succumbing finally to the 

 new conditions. The above-mentioned Ammonite, which is doubt- 

 less itself a modification of the old plicatiloid forms, would be 

 deemed Kimmeridgian if found in middle or northern England. In 

 the Weymouth district, however, the Ammonites for the most part 

 seem to occur on horizons lower than we should expect, judging 



