part 3] SUCCESSION or the atojsiais' at clifto^s^ 



217 



Small phosphate-nodules occur in certain bands (A 8), and Mr. 

 Dixon informs me that similar nodules are met with in the Lower 

 Modiola Shales of Tenb}^ 



(/;) The Upper Beds. — The upper 30 feet immediately below 

 the Br^'^ozoa-Bed are well exposed, and consist mainly of thinl}^- 

 bedded, often sandy and rubbly limestone with reddish shaly 

 partings. One limestone-band is, however, as much as 4 feet 

 thick. Certain bands in Km show some dolomitization ; but it is 

 not a characteristic feature of the rocks of this level. 



About 15 feet below the Bryozoa-Bed in the upper Avonmouth 

 line is a well-known band of argillaceous limestone, crowded with 

 Atliyris roi/ssii and containing Spirorbid annelids and bryozoa. 

 This band has not been obse]'ved in the lower line. 



On the left bank of the Avon the Modiola Shales are well 

 exposed, both in the railway-cutting and by the riverside. 



The following is the succession in the riverside exposure : — 



Thickness in feet inches. 

 Bryozoa-Bed. 

 Thinly-bedded sandy and rnbbly limestone, with reddish ~l 



shaly partings J 



Shale, with two prominent but impersistent bands of 



black limestone at the base 



Black limestone 1 



Argillaceous limestone overlain by shale 1 



Massive, finely crinoidal limestone 4 



Shale with thin irregular limestone-bands, some of which 

 are crinoidal, some algal ; while in others Spirorbid 

 annelids, lamellibranchs, and small gastropods are seen 



on the weathered surface 



Limestone, mainly algal, alternating with partings of sandy i 

 shale. One bed of algal limestone shows brecciation. J. 7 



The highest bed is ripi)le -marked j 



Sandy shale 5 



Limestone 1 



Shale ■ 6 



Green micaceous mudstone with fish-scales, overlying] 

 reddish shale regarded as the top of the Old Eed Sand- y 1 

 stone 



12 

 11 



10 



9 



8 

 7 

 6 







14 





 6 

 6 



15 



61 



The most interesting bands in the above section are Nos. 5 & 6, 

 in which the algal nodules show \vp well on the weathered 

 surface (see PL YIIl, fig. 1). In the three rock-slices examined 

 Miickeldeania, associated sometimes with OrtoneUa^ forms narrow 

 bands alternating with fine sandy material. 



Another fine section of the whole of Km is seen in the railway- 

 cutting. The development is less shal}" than that on the right 

 bank of the Avon. Immediately below the Bryozoa-Bed is a 

 band of grey crinoidal limestone which does not occur on the right 

 bank. 



