part 8J suocESSioi^ or the atoniajN" at clifton. 231 



Mitclieldeania^ often associated with Sponr/iostronia, is the preva- 

 lent organism (A 18G, 187, 188). The Concretionaiy Beds are 

 interbedded with china-stones, sometimes containing algie and 

 ostracods, and with white foraminiferal and occasionalh^ oolitic 

 limestone-bands, some of which are partly dolomitized. 



The Concretionary Beds are also seen in the riverside exposm-e 

 nearly opposite the New Zigzag level-crossing. 



Series on the right bank as repeated by the fault. — 

 The S., beds, as repeated by the Clifton Fault, form the great mass 

 of Observatory Hill (St. Vincent's Rocks), and the section extends 

 from near the bottom of Bridge-Valley Road to a point about 

 15 yards north of the wall at the base of the Old Zigzag path. 

 The whole of the S beds from a few feet below the base of the 

 Seminula Oolite is seen, and the exposures are altogether ver}^ 

 much better than in the main section. The lowest beds seen are 

 a few feet of white china-stone, followed by about 10 feet of 

 massive partlj^-dolomitized limestone, with a double layer of chert 

 in the upper beds. Above this layer, and immediately below the 

 base of the Seminula Oolite, is the band of soft dolomite in which 

 the cave of the Gi-reat Quarry occurs : this band may be easily over- 

 looked. The Semiiiiila Oolite forms practically all the lower part 

 of St. Vincent's Rocks, extending from the fault to the southern 

 end of the section behind Hot wells Station. It is not, as a rule, 

 in a good condition for examination, the exposed surfaces being 

 frequently weathered joint-faces, especially in the station enclosure. 

 The repetition of strata hj the small thrust-faults of Observatory 

 Hill gives an exaggerated impression of the thickness of the 

 Seminula Oolite. 



The lower part of the overlying beds S.^ (c) is well seen, if the 

 rocks behind the station enclosure are climbed, and also at the out- 

 crop of these beds south of the station. They consist of massive 

 grey limestone and dolomite, with abundant Lifhostrotioii and 

 GJionetes and some chert. The Concretionary Beds, S., (d)^ are 

 splendidly exposed in the big rock-face immediately south of the 

 Bridge. The base of this face is formed by the upper part of the 

 underlying strata, S^ (c), and includes china-stones, white oolites, 

 Seminula bands, and pisolite-bands; but the main part is formed 

 by the Concretionary Beds, which are seen to be thicker than an 

 examination of some of the other sections might have led one to 

 expect. They consist, in the main, of massive white limestone with 

 numerous concretionary, pisolitic, and Seminula bands and a con- 

 siderable amount of oolite. The concretionary bands show up less 

 than in exposures where the rocks are more highly weathered, 

 and the algal (concretionary) laj^ers are sometimes considerably 

 dolomitized. The best exposure of S^ (c) is in the rock-faces 

 bordering Observator}^ Hill as the Suspension Bridge is approached. 

 Here the rocks are highly fossiliferous, Carcinopliyllum being 

 especially plentiful, and algal limestones (/S'e;;^/;^^/^ -pisolite struc- 

 ture) extremely well seen. 



