GRAPTOLITES. 

 BY PROFESSOR C. LAPWORTH, F.R.S., Birmingham University. 



THE Silurian strata of the Basin of the Firth of Clyde contain some of the 

 richest graptolite-bearing deposits in the world, and the Graptolites which 

 they afford include examples of all the known families of this group 

 of fossils. 



Researches carried on in the region of the Southern Uplands of Scotland 

 (a portion of which lies within the limits of the Basin of the Clyde) first 

 demonstrated the reliability of Graptolites as " zone fossils " for unravelling 

 the sequence of the British Lower Palaeozoic deposits : and within the last 

 thirty years these fossils have been keenly studied by foreign geologists and 

 palaeontologists in Scandinavia, France, Bohemia, Belgium, Canada, the United 

 States, etc. In these countries, as in Britain, their first-rate importance 

 as aids in working out the geology of the older stratified rocks has long been 

 admitted and utilized. Geologists owe it to the Graptolites that they are now 

 able to divide the Ordovician and Silurian strata into successive chronological 

 " life zones " corresponding with those demonstrated by means of the 

 Ammonites for the Jurassic sediments more than half a century ago, and 

 to parallel satisfactorily the strata containing them in Britain with the 

 equivalent deposits in Europe and America. 



The region of the Southern Uplands of Scotland of which the basin of 

 the Upper Clyde forms a part is the type region for these fossils in Britain 

 from the stratigraphical point of view. The recent Memoir of the Geological 

 Survey ("The Silurian Rocks of Britain," vol. i., 1899) gives an admirable and 

 detailed account of the distribution of Graptolites in the southwest of 

 Scotland, and of the geology of the Southern Uplands. To this work the 

 reader is referred. 



Graptolites are especially abundant in the Silurian rocks of the basin of 

 the Upper Clyde at the localities of Wanlockhead and the Leadhills. 

 Here they constitute the predominant fossils of the district, and are prac- 

 tically confined to certain black shale bands which run through the 

 country along the strike of the beds. They are also present, in less abund- 

 ance, however, in the Silurian strata of the coastal district of Girvan ; but 

 here they are often associated with crowds of other fossils Brachiopods, 

 Trilobites, Cephalopods, etc., and are more generally distributed throughout 

 the entire succession. 



In the Guide Book issued for the members of the British Association at its 

 last meeting in Glasgow in 1876 ("Catalogue of Western Scottish Fossils," 

 J. Armstrong, J. Young, and D. Robertson) four plates by the writer of 

 figures of the more characteristic Scottish Graptolites were included. 

 Figures of the common Scottish forms have also been published elsewhere. 

 See for example the Proceedings of the Belfast Naturalists' Field Club* 

 Appendix, 1876-1877, and the plates in the Survey Memoir, 1899, cited above. 



