part 3] SUCCESSION of the ayo:sian at cliftox. 219 



example of a dolomite met with in the K beds of the Avon 

 Section. 



Mr. E. E. L. Dixon ^ discusses the conditions under which 

 ferruginous limestones of the Biyozoa-Bed type accumulated, 

 concluding that they were deposited in shallow water in isolated 

 coastal areas. 



On the left hank of the Avon the Brjozoa-Bed is well seen, 

 both in the railway-cutting and in the riverside exposure. 



(8) Kj. (Thickness = about 7U feet.) — Only the lower part of 

 K^ is exposed on the right bank of the Avon, being seen in the 

 lower Avonmouth line. The Bryozoa-Bed is here succeeded by 8| 

 feet of thinly-bedded sandy limestone, and then comes the well- 

 known ' Palate-Bed,' a gritty crinoidal limestone about 6 inches 

 thick, containing brj^ozoa, numerous palatal teeth of Elasmobranchs, 

 and rounded nodules of phosphate (' coprolites '). This band is 

 also exposed under the arches near the mouth of the tunnel, on the 

 upper Avonmouth line. On the Palate-Bed rest a few feet of rock, 

 partly consisting of fine calcareous grit with grains of a green 

 mineral (probably vivianite), but passing up into somewhat gritt}^ 

 limestone with crinoids, many brachiopods, and small phosphate- 

 nodules. Then follow 20 feet of ill-exposed shale and thinly- 

 bedded limestone containing abundant brachiopods and ostracocls, 

 sometimes associated with crinoids and bryozoa. One band is 

 crowded with bryozoa and small gastropods, and structures believed 

 to be Echinid-spines occur (A 34). 



The remainder of the section, as far as the point where a path 

 crosses the railwaj^ is hidden by a wall, and it is at the path that 

 Yaughan (Avon jDaper, p. 98) drew the line between K^ and K,,. 

 Miss M. B. Chapman gives analyses of two rocks from this 

 horizon, and records the presence in the insoluble residue of zircon, 

 tourmaline, and much kaolinized felspar. 



On the left bank of the Avon the greater part of Kj^ is seen in 

 the riverside exposure. A few feet immediately overlying the 

 Bryozoa-Bed are not exposed, and the Palate-Bed is not seen. 

 Then come 11 feet of thinly-bedded limestone with shaly partings; 

 some of the limestones are compact and not obviously fossiliferous, 

 but most are crowded with brachiopods. Two bands near the top 

 of this layer are noteworthy : a lower one full of Ortliotefes 

 crenistria, the cavities of the shells being occupied by conspicuous 

 white patches of crystalline calcite, and an upper one crowded with 

 Lepfcena ana log a . 



Shales and mudstones, 17 feet thick, with subordinate thinly- 

 bedded, compact, and not markedly fossiliferous limestone succeed ; 

 then follow perhaps about 20 feet of ill-exposed limestone and 

 subordinate shale. The limestone generallj^ is highly fossiliferous. 

 CJeistopora geomeirica occurs at this level less rarely than else- 

 wdiere in the Avon Section. 



^ Q. J. G. S. vol. Ixvii (1911) p. 515. 



