230 PEOF. s. H. eet:n'olds oy the litholooical [vol. Ixxvii, 



rocks foriniDg the wall at the southern end of the Great Quany 

 behind the liring platform, and easily accessible on the crags to 

 the south, are chielij massive foraminiferal limestones, but include 

 Lithostrofion- and Clio}ietes-h2a\dis, the two fossils being often 

 associated and the matrix between them more or less dolomitized. 

 The rocks of this level further include fairly massive beds of 

 dolomite, and a band of pisolite exposed rather high up the 

 quaiTV-face. The limestones forming the main part of the big- 

 weathered rock-face immediately south of the cpiarry are also 

 included in this division. This rock-face is a joint-face covered 

 with calcific and flmty vein -stuff and breccia, to such an extent 

 that little can be made out in the field as to the character of the 

 rocks, and it is even difficult to break off pieces. There are, 

 however, a few exposures in the wooded slope below the rock-face, 

 and others may be reached up the quarry-side. Sections show 

 that the rocks include foraminiferal limestones, sometimes partly 

 oolitic (A 12S <7) ; while algal china-stones are frequent, some 

 being partly dolomitized. The upper part of S^ (c) is. however, 

 far better exposed in the series as repeated by the fault. 



S.,(t/). The Concretionary Beds. (Thickness ^about 125 

 feet.) — These rocks are fairly well seen above the wooded slope 

 south of the Great Quarry, and can be followed down to the railway 

 near the Xew Zigzag path. They are thinner than north of Bristol 

 at Brentry and Sodbury, and the poor character of the exposures 

 has probably caused them to be considered thinner than is actually 

 the case, for the concretionary structure comes on some do feet 

 lower than the line marked as the base of these beds in pi. vii 

 of Vaughan's Avon paper. The character of the Concretionary 

 Beds, first mentioned by H. B. Woodward,^ was fully described by 

 Yaughan in the above-quoted paper (pp. 91-92), but no opinion 

 was expressed as to the origin of the concretionary structure. In 

 the Burrington paper,^ however, its probably algal nature was 

 recoD'nized. In describino; the Beloian rocks Vauo-han ^ ao;ain 

 refers to these beds, regarding them as a modification of the 

 ' calcaire zonaire ' of Dr. H. de Dorlodot. 



Many of the 'concretions ' strongly resemble the GirvaneUa- 

 nodules described b}^ Prof. Garwood ^ from the D., beds of 

 Humphrey Head, Grange. Sections, while, hoAvever, confirming 

 the essentially algal character of the concretions, show that 



^ ' On Arborescent Carboniferons Limestone from near Bristol " Eep. Brit. 

 Assoc. (Bristol) 1898, p. 869, and Geol. Mag. 1899, p. 77. The author describes 

 a specimen of the Concretionary Beds from near Brentry, attributing* the 

 curying character of the layers to disturbance, not original deposition. He 

 suggests comparison with the Gotham Marble, and adds : ' The appearances 

 are probably due to mechanical disarrangement of the upper layers produced 

 prior to and during the consoKdation of the rock, and they suggest a j)ause in 

 the deposition of sediment.' 



- Q. J. G. S. vol. Ixrii (1911) p. 34.5. 



^ Ihid. vol. Ixxi (1915) p. 26. 



^ Ihid. vol. IxYiii (1912) p. 482. 



^ 



