236 PROF. S. H. EEY^'OLDS OX THE LITHOLOGICAL [vol. Ixxvii, 



Turds north of the Old Zigzag path to the end of the section near 

 the Colonnade. The rocks consist of a lower series of white lime- 

 stones overlain hy rubbly limestone and pseudobreceia with shalj 

 partings. The highest beds are largely coarse oolite. There are 

 good exposures by the sides of the Zigzag path, pseudobreccias 

 being well seen near the top of the path. 



Exposures of the D ihiuioj^^i^IIu^n Beds 

 on the left bank. 



The main section. — The beds forming the cliff at the top 

 of the tunnel-slope south of Quarry 5 are the base of D^. The 

 cliff-boundary is determined by a big calcite-vein in the lower 

 part of Dj, and is in a very bad state for examination. There are, 

 however, at the base of the cliff many fallen blocks of D^, which 

 have separated off along shaly partings, and these form a good 

 collecting-ground. The dip brings the Dj beds from the top of 

 the tunnel-slope down to the road, near a small jDadlocked building, 

 where they are well exposed. The prominent bedding-planes south 

 of this building are determined b}' bands of pseudobreceia,. and are 

 mentioned by Vaughan as good D^ collecting-ground. The D^ 

 beds are splendidly exposed in the riverside section adjacent to the 

 tunnel-slope, and consist of massive white limestone alternating 

 with pseudobreccias and with red shaly partings containing gigan- 

 toid Producti. The pseudobreccias form conspicuous bedding- 

 planes covered with Cyatliopliijlhim murcliisoiii, Lifhosfrotion, 

 and less coTawiovilj Alveolites sejJtosa. Corals are nearly as plentiful 

 in the massive limestone. The riverside exposure affords a section 

 of these rocks over 100 j^ards long. Xo more exposures are met 

 with until Quany 6 is reached, Avhere D^ limestones, in part grey 

 and massive, in part pseudobrecciated, and in part coarsely oolitic, 

 occur, but could scarcely be in a worse state for examination. 



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

 The D beds are very poorly exposed by the railway between the 

 Suspension Bridge and Clifton -Bridge Station. Xot far south of 

 the bridge there are fair exposures of white limestone with D^ 

 corals, while farther south the chief exposures are of the massive 

 grit-bands of Upper D^ and D^. 



III. Changes which hate afeected ceetaix of the Eocks. 



(1) Penecontemporaneous brecciation (desiccation- 

 breccia tion) is a characteristic feature of all the Jiof/Zo/r^'-phase 

 rocks. It affects some of the algal bands in Km, and is met with 

 at intervals throughout the Can in in Dolomites (C^) and the whole 

 of the Seminula Beds. The most noteworth}" bands showing this 

 feature are (1) a coarsely-brecciated band at the base of the 

 CcDiiaia Dolomite; (2) the various Seniinida-VisolitQ levels; 

 (3) the bands at the top of the Seniimda Oolite exjDOsed near the 

 firing platform in the Great Quarry. It is, however, sometimes 



