On the Corallian Rocks of England, 155 



feroua towards the top, clays and grits. Another section, on the oppo- 

 site side of the anticlinal, shows the same development of the central 

 limestones ; hut tho lower series is considerably attenuated, and the 

 upper series (Supra-Coralline) shrunk from about 90 feet to a thin 

 ferruginous band of only a few inches. There are hardly any 

 corals, and no Coral Hag whatever ; argillaceous and arenaceous 

 matter (always, however, more or less mixed with lime) prepon- 

 derates ; but there is a rich and varied fauna, which has strong 

 affinities with some of the Coralline beds of other districts. This 

 culminates in the Trigonia-beda, which lie towards the top of the main 

 limestone series ; above this the fauna inclines to Kimnieridgian, 

 below to Oxfordian types. The remarkable irregularity of the 

 Supra-Coralline beds was noted, especial reference being made to the 

 mineral character, fossil contents, and geological position of the 

 Abbotsbury iron-ore. In the North-Dorset district (II.) the thick- 

 ness of the mass is much reduced, and its constitution greatly 

 altered. Corals are still very rare ; but calcareous sediment greatly 

 preponderates, and is made up largely of comminuted shells, 

 loosely aggregated pisolites, and rubble frequently false-bedded. 

 The arenaceous base of the Corallian series, described generally under 

 the term Lower Calcareous Grit, is almost at its minimum in the 

 neighbourhood of Storminster. The central limestones contain a 

 moderate assemblage of the usual Coralline forms, but Cidan's 

 florigemmci appears confined to a rubbly bed about 8 feet thick. 

 The West-Midland range (III.), extending from Westbury to Oxford, 

 exhibits the greatest variety, and, being classic ground, contains a 

 larger proportion of the type forms of the rocks. The development 

 is very unequal ; and the entire group is reduced to less than 25 feet 

 in some places ; but where the sandy base is expanded, as in those 

 districts where the escarpment faces the north, the thickness ex- 

 ceeds 100 feet, occasionally falling to about 30 feet in the direction 

 of the dip, with the probability of the entire mass ultimately 

 thinning to a feather edge. In many places true Coral Rag is 

 largely developed, usually terminating the Corallian series in an 

 upward direction, or at most succeeded by a very few feet of ferru- 

 ginous sand. Throughout the great escarpment facing the upper 

 valley of the Thames the lower arenaceous member predominates, 

 though much mixed with thin-bedded sandy clays, the whole con- 

 stituting a loose formation, which is capped by hard gritty lime- 

 stone containing an abundant fauna, representative of the middle 

 series, differing somewhat, on the one hand, from the Rag with 

 its partially Kimmeridgian character, and, on the other, from 

 the Lower Calcareous Grit, whose affinities are, of course, Ox- 

 fordian. The beds of this district, however, are so varied that 

 it is impossible to deal with them in an abstract. District IY. 

 includes the Coral reef at Upware, 75 miles E.1ST.E. of Oxford; 

 though the exposures are small, they are very suggestive. The 

 limestone of the south pit is an excellent Coral Rag, but softer and 

 more chalky than much of the Coral Rag of the West-Midland 

 district. Moreover, whilst the rock contains many familiar forms, 

 and especially Cidaris florigemma, whose presence in abundance 



