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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Feb. 5, 



contain are indeed sufficient to settle this point, whilst the Maclurea 

 is a good Lower Silurian type in North America. 



Looking at the tract in which these insulated masses of limestone 

 occur as one of powerful eruption, it is natural indeed we should find 

 still older rocks brought to day than any which are visible in the 

 tracts on the banks of the Girvan Water, where the igneous rocks are 

 much less rife. The limestones of the Stinchar are, therefore, to be 

 considered simply as insulated masses of Lower Silurian, which have 

 been forced into their positions along sharp anticlinals, assisted by 

 the action of the copious igneous rocks ; which have disjointed them 

 from the conglomerates, sandstones, and schists of the Girvan district. 

 It is fair, therefore, to infer, that the protrusion of these limestones 

 with their underlying schists marks two other sharp undulations or 

 anticlinal lines. Thus, in prolonging the strike of the Bogang rock, 

 it is found to be coincident with the Aldeans quarry and the whole 

 course of the Upper Stinchar above its junction with the Assell ; 

 whilst the anticlinal of the Craig Neil limestone coincides with the 

 course of the Lower Stinchar from Pinwhirry Castle to the sea (see 

 Map). 



The occurrence of five or six axial lines in a traverse of less than 

 eight miles directly across the strata is an important feature which 

 will be afterwards dwelt upon. In the mean time, it may be said, 

 that the Ayrshire Silurians contain evidences both zoological and 

 stratigraphical (the one method helping us where the other fails), to 

 show that some of their strata are of the age of the Llandeilo or 

 Bala limestone, whilst others, including the conglomerates, belong to 

 strata extending upwards to the zone of the Caradoc sandstone. 

 Whether the orthoceratite schists and flagstones will also be classed 

 with the Lower Silurian, or form the base of the Upper Silurian rocks, 

 must be a subject of future discussion ; although it is manifest that 

 all these subdivisions here form one natural group only. 



The only point of detail on which my associate, Professor Nicol, en- 

 tertains a different opinion to that which I have suggested, is that 

 he surmises that the shelly sandstones (2) of Saugh Hill may overlie 

 the orthoceratite-flags (1). He grounds his view on the impression 

 which he has taken of the physical structure of this much-obscured 

 tract, and, as he was disposed to think that ulterior researches might 

 establish his view, I presented his two ideal sections of the coast and 

 the interior to the Geological Society. I cannot, however, admit the 

 possibility of separating the conglomerate from the shelly sandstones ; 

 because in this very tract of Scotland I saw pebble-beds intercalated 

 and repeated in that, which from its fossils I consider to be the equi- 

 valents of the Caradoc or Llandeilo sandstones, passing down into 

 limestone of the age of Llandeilo and Bala ; in one spot forming courses 

 immediately above the lower limestone, in another recurring at different 

 horizons in the ascending order, until they form, as at Kennedy's 

 Pass, the very remarkable mass which supports the flagstones and 

 schists with Orthoceratites and Graptolites. 



