Vol. SS."] SUCCESSION IN THE NOETH-WEST OP ENGLAND. 487 



The SoUnopora Siib-zoue. — The beds overlying the cod- 

 gloinerate in the Shap-Abbey section consist of 60 feet of 

 compact cement-stones and dun-coloured magnesian limestones with 

 partings of shale (see PI. XLIY, fig. 1). Under the microscope 

 many of the beds are seen to contain quartz-grains, and to be rich 

 in the remains of foraminifera. The following is a typical per- 

 centage analysis ^ of the dun limestones : — 



CaCO, 71-13 



MgCOg 19-72 



FeO, etc 1-78 



Insoluble residue 7 "37 



Total ... 100-00 



The origin of the magnesium carbonate has already been 

 discussed (see pp. 457-458). 



The shale-band which occurs about half-way up the cliff is 

 crowded with the remains of bryozoa and the flattened shells of 

 Atliyris glabristria still bearing their fringe-spines, A Solenopora 

 Band occurs in the lowest limestone immediately below the bryozoa- 

 shale, and another similar layer is seen near the top of the cliff. 

 It is interesting to note that the specimens of Solenopora show 

 no trace of dolomitization, notwithstanding the fact that the matrix 

 ill which they occur is highly dolomitic. Miss K. Eurke, B.Sc, of 

 University College (London), to whom I am indebted for analyses 

 of specimens of Solenopora from this section, finds that they contain 

 over 99 per cent, of calcium carbonate. This fact would "appear to 

 ])oint to the process of dolomitization having been selective, and 

 nffords food for speculation regarding the original composition of 

 the thalli constituting these organisms, since among living cal- 

 careous algse some are formed of aragonite and others of calcite. 

 It is possible, however, that the markedly compact character of the 

 Solenopora nodules may have enabled them to resist alteration ; 

 while the fragments of brachiopods and other organisms have been 

 more readilj^ dolomitized.^ Athyris glabristria occurs abundantly, 

 nnd forms a band at the top of the cliff. Dr. Yaughan, who has 

 Idndly examined specimens from this locality, reports that many of 

 these resemble closely forms from Z., of the Bristol District. The 

 general fauna of this sub-zone has already been tabulated (see 

 p. 460). 



The CamarotoecJiia-proava Band crops out a few yards 

 back from the top of the cliff; it is poorly developed here, and 

 has not been traced any farther in a northerly direction. To the 

 south-east, however, the zone increases in importance, and in the 

 neighbourhood of Eayne the band is crowded with the index-fossil. 

 At the base of this bed occurs a layer largely made up of plates 



1 For this and other analyses I am indebted to Miss Winifred May, B.Sc, 

 and Mr. M. R. Eeid, of University College (London), 



^ The Girvanella nodules at the base of the Upper Bihiinophyllum Sub-zone 

 on the other hand, are frequently much more highly impregnated with haematite 

 than the surrounding matrix. 



