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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 5, 



described by Professor Phillips as occurring in black schists on the 

 south-west flank of the Malvern Hills, which I formerly placed as 

 Lower Silurian rocks. In Bohemia, which, of all countries in the 

 world yet examined, exhibits, under the masterly delineation of M. 

 Barrande, by far the most complete development of Silurian life, from 

 its commencement to its close, the same band with Olenus and other 

 fossils reposes, as in North Wales, on a vast thickness of azoic rocks, 

 and is surmounted by the equivalents of the Llandeilo and Caradoc as 

 well as by Upper Silurian formations. Now, in the South of Scot- 

 land no fossils have been discovered which clearly point to a lower 

 horizon than that of Llandeilo ; whilst many of the shells (in Ayrshire 

 at least) would seem rather to belong to what I should call the supe- 

 rior division of the lower group. In using the term ' Caradoc sand- 

 stone ' I must not be misunderstood. I know that the valuable re- 

 searches of Professor Ramsay in the Silurian region and the adjacent 

 parts of Wales have shown that much of what 1 formerly included in 

 the Caradoc subdivision pertains rather to the Llandeilo group, both 

 by physical association and by its unconformity to the Caradoc sand- 

 stone of Shropshire. It is therefore probable, that some of the 

 Scottish shelly sandstones and conglomerates may represent such 

 " Llandeilo Sandstones." Time and much close work can alone 

 decide such points as these. But the essential consideration is, that 

 even in Wales the overlap, elucidated by Professor Ramsay, has made 

 no change in the upward development of animal life. All is Silurian. 

 At least, many of the Upper Caradoc, and even of true Upper Silu- 

 rian fossils have, it appears, existed in the period when the Llandeilo 

 or Bala limestone was formed. In comparing Scottish and other 

 distant rocks with those of Silurian age in England and Wales, we can, 

 as I have all along contended, speak only of two great zoological divi- 

 sions, the Upper and Lower Silurian forming one natural system*. 

 This inference is sustained not only by reference to well-known En- 

 glish and Welsh types, but also to Irish fossils from Galway and other 

 places, where a number of Lower Silurian species are associated with 

 many forms characteristic of the Upper Silurian rocks f . 



Thus, whilst the Ayrshire limestones may very well be considered 

 as on the same horizon as the Llandeilo and Bala limestones of South 

 and North Wales, the shelly sandstones and conglomerates of 

 Girvan are representatives of all the strata upwards which I regard as 

 Lower Silurian, including the Caradoc sandstone ; whilst the schists 

 and flagstones with Orthoceratites and Graptolites, though I say it 

 very doubtfully, may either represent the uppermost band of the 

 Lower group, or the very bottom beds of the Upper Silurian rocks. 

 In their undulations southwards these latter rocks become more de- 

 veloped, and, in unfolding a great thickness of graptolite -schists, ex- 

 pose the fossil bands of Kircudbright Bay, which are in all proba- 

 bility of the age of the known Wenlock shale. 



* See Silurian System, p. 195, 308, et passim; Russia in Europe, vol.i. ch. 1 and 2. 



f The steady strike of the fossiliferous Silurian rocks is seen in the Pentland 

 Hills, in the greywacke of which Mr. Maclaren detected Orthoceratites. Although 

 much obscured there by powerful masses of porphyry (all the intermediate country 

 being occupied by coal-fields and trap), the Ayrshire zone of Silurians may be con- 

 sidered to reappear in the Pentland Hills on the true bearing to E.N.E. 



