148 Geological Society: — 



by a coarse boulder-conglomerate, and containing hosts ul 

 Brachiopoda &c., chiefly Meristella angustifrons, Atrypa 

 hemisphceriea, Nidulites favus, &c. 



(II.) Lower Girvan Rocks. 

 (B.j Abdmilla>- Seeks (1800 to 2000 feet), embracing the 



(4) Drummuch Group of soft grey mudstones &c, with Trim*' 

 clcus seticornis, Ampyx, Staarocep>halus, Dicellograptus, dec. 



(3) Barren or SJmlloch Flagstones. — A great thickness of alter- 



nations of grey or green flagstones and shales, generally 

 destitute of fossils. 



(2) WhiieTwuse Group. — Purple and green shales and mud- 

 stones, striped flagstones and calcareous beds, with Dionide, 

 Dindymem, JSglina, Agnostus,Dktyonema, Dicellograptus, 

 and PUurograptus. 



(1) The ArdweU Group of dark Graptolitic flagstones and 



shales, with occasional fossiliferous seams affording 

 examples of Dicranograptus, Leptograptus, and Glimaco- 

 graptus, &c. 



(A.) Babb Series (800 to 1000 feet), composed of the 



(4) Baldatchie Beds. — Highly fossiliferous pebbly grits and 



nodular shales, with Lingula Bamsayi, L. canadensis. 

 Siphonotreta rmcida, Bemopleurides, Glossograptus, Sx. 



(3) Benan (or Green) Conglomerate. — ^Massive boulder-beds of 



great thickness, unfossiliferous. 



(2) Stinchar (or Craighead) Limestone Group, composed of 



compact limestones, nodular and calcareous flagstones and 

 shales, with Maclurea Loga.nl. Ophileta, Orthis con finis. 

 Tetradium, Lidymograptus, Clathrograptv.s, &c. 

 (1 ) Kirkland (or Purple) Conglomerate. — Coarse boulder-beds 

 and sandstones, generally of a purple colour. 



It was shown that the highest beds of this succession are faidted 

 against strata of Carboniferous age. The discussion of the relation- 

 ship of its lowest beds to the igneous and metamorphic rocks of 

 Ballantrae was deferred to a future paper. The author pointed out 

 how perfectly this reading of the succession explained the anomalies 

 hitherto supposed to obtain among the fossils of the Girvan region. 

 When the organic remains collected from these strata by previous 

 investigators (notably the magnificent Gray collection) are referred 

 to their natural horizons in this stratigraphical succession, it is 

 found that each of the great penological divisions of the Girvan 

 series has a collective fauna peculiarly its own, and that the general 

 zoological gradation is identical with that of the acknowledged 

 sequence in the typical Lower Palaeozoic areas in "Wales and the 

 "West of England. 



The Lower Girvan rocks are clearly of Ordovician age : while the 

 Upper Girvan rocks as distinctly appertain to the Silurian. The 

 Barr Series corresponds to part of the Llandeilo-Bala of Wales \ and 



