C— GEOLOGY. 77 



marked phases or sub-phases, and the whole series may be classified 

 as follows : — 

 Predominantly limestone. 



1 . Standard phase. 



2. Modiola phase (calcareous lagoon-phase). 



3. Reef-kuoll phase (including the ' brachiopod beds ' of the Midlands). 

 Partly limestone, partly shale. 



4. Zaphrentid and Cyathaxonid phase. 

 Predominantly shaly. 



5. Goniatite-lamellibranch or Culm phase. 



6. Radiolarian phase (siliceous lagoon-phase j. 



7. Shale phase. 



Variable — limestone, shale, sandstone, and sometimes coal. 



8. Yoredale phase. 

 Sandy. 



9. Massive sandstones. 



Of these Nos. 2, 4, 5 and 6 have already been defined, Nos. 7 and 9 

 require no definition, while No. 3 is defined in the sequel. 



The standard phase may be said to consist of limestone, frequently 

 coarse-grained or crystalline, in which fossils are commonly abundant. 

 Some of the chief varieties are crinoidal limestone, coral limestone and 

 brachiopod limestone. Foraminiferal limestone and oolite link these 

 rocks with those of the calcareous lagoon-phase. 



The Yoredale phase. — The limestones are sometimes of standard, 

 sometimes of Zaphrentid phase type, and include also calcite mudstones 

 and algal limestones. The standard limestone fauna may be a coral- 

 brachiopod assemblage, or may be mainly a brachiopod fauna or mainly 

 a coral fauna. The fauna of the associated shale may be very much 

 that of the shales of the Zaphrentid phase, but sometimes bands with 

 the goniatite-lamellibranch fauna occur. 



The Cement Stones of the Northern Province have features linking 

 them to the Zaphrentid phase and to the Yoredale phase. They consist 

 of thin-bedded sandstone and shale, the latter often highly coloured, with 

 bands of argillaceous limestone or cement stone, which is sometimes algal. 

 The fossils, which are somewhat scanty, are mainly of shallow-water 

 type — spirorbids, ostracods, horny brachiopods, and small lamellibranchs 

 and gastropods. 



'Millstone Grit.' 



As has been emphasised by Prof. Kendall,^^ the rocks alluded to under 

 the name of Millstone Grit are the most difficult of all the members of the 

 Carboniferous series to reduce to any systematic arrangement. The term 

 has been, and still frequently is, used in a purely lithological sense, as 

 indicating the prevalentlj' sandy rocks which sooner or later succeed the 

 prevalently calcareous or sometimes argillaceous rocks of the Avouian. 

 Any general account of the Millstone Grit is quite outside the scope of this 

 address, which will be concerned merely with the n'latious of the Millstone 



'* Handbuch der re.gionahn Gcnl., iii., 1, s. 153. 



