382 J. F. BLAKE AND W. H. HUDLESTON OX 



series as follows : — First, sands and grits well developed everywhere, 

 but especially at Nothe Point, where they are 30 feet in thickness, 

 and characterized by abundance of Perna quadrata and Pecten Jibrosus 

 — the " jSTothe grits." This portion is separated by thick masses of 

 clay (" Nothe clays ") from an upper grit (the " Bencliff grit "), in 

 the base of which are huge doggers, by which its presence may be 

 sometimes recognized, the whole forming together what would else- 

 where be called Lower Calcareous Grit. This part may be equally 

 recognized in Sections II. and III. The next series, consisting of 

 oolites and marls, and including the remarkable " Osmington Oolite," 

 is perfectly distinct in character from the overlying limestones. It may 

 be seen by the sections to vary its character even within the district, 

 at AVeymouth being least marked, and at Abbotsbury, though very 

 unf ossiliferous, being largely composed of compact beds of oolite. The 

 fossils are peculiar, but have a relation rather with the Lower Cal- 

 careous Grit than with the upper beds. These latter are the main 

 limestones of the district, but in general show but little oolitic struc- 

 ture, Osmington affording an exception; they are usually rather 

 rubbly or hummocky in character, and contain corals, but they do 

 not constitute a " Coral Rag," and contain much sandy material. 

 They are richly fossiliferous, and show a decided change of type, 

 their relations being upwards. From the abundance of Trigonia 

 davellata, we have called them the " Trigo ma-beds." Cidaris flori- 

 gemma occurs in them but rarely, while it occurs more commonly 

 in a higher horizon here ; and the other fossils are not entirely those 

 that are elsewhere associated with corals, but are partly found 

 below them. Above the main limestones at Weymouth we have 

 a great thickness (40 feet) of clay, which we call Sandsfoot 

 Clay, overlain by ferruginous sands and grits of very remarkable 

 character, both in lithology and fossils, having large spongeous 

 growths, and containing Cidaris florigemma, Lima pectiniformis, 

 Lingida ovalis, Littorina muricata, Astarte supracorallina, and many 

 other fossils which are generally associated with corals, or rise to 

 higher zones. All this is well represented, as far as can be seen, at 

 Abbotsbury (Section III.), and somewhat inconspicuously and of 

 less thickness at Osmington. In Eingstead Bay a remarkable Upper 

 Coral Rag is developed above these grits and immediately below the 

 Kimmeridge passage-beds. On a higher horizon, perhaps, than any 

 of the Corallian rocks of the rest of the district comes the Abbots- 

 bury ironstone, alike remarkable for its peculiar character and 

 abundant Brachiopods, which are elsewhere almost absent from the 

 Corallian beds. The great feature of this district is the limitation of 

 any thing that can be called a coral reef to a very small area ; while 

 the changes that have taken place in the characters of the deposits, 

 which are, on the whole, of great thickness, are exceptionally 

 numerous. 



J^orth Dorset. — In this district we have considerable variety in 

 the Corallian development. In the southern part of it (Section IV.) 

 there is a very little Lower Calcareous Grit, its place being taken 

 by a continuation downwards of oolites and marls with beds 



