part 3] succESSioiN' or the ayoxiaat at clifton. 235 



alternating with thick shales and red grits. There are bands of 

 both oolite and grit upwards of 20 feet thick. The shale-bands, 

 though not well exposed, attain a great thickness. 



Attention may be drawn to a band of red non-oolitic limestone 

 full of Product us liemisplKEvicus^ which is exposed in the cutting 

 45 3"ards north of the tunnel. Specimens from this bed are 

 common in old collections. 



The grits, which are finely granular and iron-stained, often 

 contain some calcareous matrix (A 143). One band consists of 

 large oolitic grains mingled with almost equally large quartz- 

 grains (A 151). 



(2) D.,. The Upper D ihu nopli i/U u in Beds. (Thickness 

 =about 184 feet.) — The D.^ beds are well exposed by the road 

 between Point Villa and the fault, and are also seen in the river- 

 side exposures. The upper beds of the Bridge-Valley Koad section 

 belong to this horizon. Almost at the base of D, is a coarse grit 

 (A 154) enclosing quartz-pebbles an inch long : this is the only 

 example of such a conglomeratic rock met with in the Avon 

 section. Apart from this band, D^ is almost identical lithologically 

 with Dp including thick red grits, shales, coarse oolites, and 

 foraminiferal limestones, together with bands of "pseudobreccia 

 and rubbly bands containing Lifhostrotion irregiilare (A 161). 



At about 25 feet from the top of the D., section, as exposed by 

 the roadside at the bottom of Bridge-Valley Road, an interesting 

 band of sandy limestone occurs. The rock is a variety of pseudo- 

 breccia in which recrystallization has led to the concentration of 

 sandy and ferruginous material in the ' matrix ' ; wdiile in the more 

 usual type of pseudobrecciation it is argillaceous material that is 

 so concentrated. The rock appears to be similar to one variety of 

 the ' Spotted Beds' described by Prof. E. J. Garwood ^ from the 

 North- Western Province. Weathered blocks built into the wall 

 near the bottom of Bridge-Valley E-oad show the characters of the 

 rock to perfection. 



Crinoids, though not abundant in D,,, play a more important 

 part than in D,, and reach a greater size than in any other part of 

 the Avon Section. Corals are more varied and abundant at certain 

 levels in D^ than at any other horizon, and are well seen in road- 

 side exposures south of Point Villa. One band is crowded with 

 bryozoa. At certain levels (A 159) there has been some dolomi- 

 tization, the change particularly tending to affect the matrix 

 between the oolitic grains. The uppermost much disturbed beds 

 seen at the mouth of the tunnel and immediately below the thrust- 

 plane of the Observatorj^-Hill fault are mainly red shales and thin 

 grits. 



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

 The lower D^ beds are well exposed, and extend from a point a few 



1 Q. J. G. S. vol. Ixviii (1912) pp. 475-77. 



