Yol. 67.] THE AVONIA.H OF BUERINGTON COMBE. 35$ 



of the grains developed round bits of crinoid-stems. The peculiar 

 pisolite-breccia is confined to the S beds. 



Foramini feral limestone. — Foraminifera are the principal 

 limestone-builders throughout C 2 , S 1? and much of S 2 . A large 

 proportion of the oolitic limestones are strongly foraminifera! ; 

 but, especially in G , there is much limestone abounding with 

 foraminifera and yet not oolitic. H. B. Brady, in the Introduction 

 to his Monograph on the Carboniferous and Permian Foraminifera 

 (Pal. Soc. 1876), after referring to various deposits, such as the 

 White Chalk and the ISTummulitic Limestone, as being formed almost 

 exclusively of the remains of foraminifera, says that in Britain 

 no portion of the vast series of beds known as Mountain Limestone 

 has any claim to be placed in the same category, except the 

 Saccammina Limestone (p. 4). This statement does not hold good 

 with regard to the rocks at Burrington, some parts of C 2 being 

 probably as foraminiferal as the Chalk. As regards the genera of 

 foraminifera present, EndotJiyra, Valvulina, and Trochammina 

 appear to be the commonest, and have been found at numerous 

 levels from the base of C., to the top of S„. Tenctularia is the next 

 commonest, and JSodosaria has been noted at several levels. 



Coral-limestone. — Coral-bands are prominent at the following 

 levels : — 



(«) In D, : where certain bands contain Dibunophyllum and Cyatho- 

 phyllum in abundance. 



(h) In S 2 and at the base of S x : where Lithostrotion martini occurs in 

 large masses, and is the main component of thick beds of lime- 

 stone. 



(c) In Ci below the dolomitized beds : here Caninia cylindrica is very 

 abundant. 



Brachiopod limestone. — Throughout the Seminula Zones 

 bands crowded with Seminula are frequent ; and, in places, as 

 near the top of S 2 , bands composed of giganteid Producti occur. 

 There is a marked band of papilionaceous Chonetes at the base 

 of the dolomites of C r Bands full of Spirifer clathratus and 

 Chonetes hardrensis are a feature of Z 1 and Z 2 . Brachiopods almost 

 vie in importance with crinoids as limestone-builders in K. 



Crinoidal limestone. — Crinoids are the prevalent limestone- 

 builders throughout Iv, Z, and C x . They also play an important 

 part at the base of D x and C . 



Polyzoa are sufficiently plentiful at certain levels in K 2 to form 

 an appreciable constituent of the rock, as are ostracods in K 1 . 



Dolomite forms the upper part of C 1 , and local and subsequent 

 dolomitization has taken place at various points in the S beds,, 

 probably by the percolation along certain divisional planes of; 

 water containing magnesium carbonate. 





