74 Geological Society. 



study of the fossil vertebrates of Spain, followed by a classified list 

 of the species (68 in number) which have been recognized in that 

 country. The author particularly remarked on the occurrence of 

 Sivatherium and Hyamarctos in Spain, on the finding of remains of 

 the Mammoth in that country, and on the presence in the peninsula 

 at a late period of Bos primigenius. The earliest known Spanish 

 vertebrates have been obtained from the Carboniferous formation. 



December 6, 1876.— Prof. P. Martin Duncan, M.B., E.P.S., 

 President, in the Chair. 



The following communication was read : — 



" On the Intrusive Character of the Whin Sill of Northumber- 

 land." By W. Topley, E.G.S., Assoc.Inst.C.E., Geological Survey of 

 England and Wales, and G. A. Lebour, F.G.S., Lecturer on Geological 

 Surveying at the University of Durham College of Science, New- 

 castle -on-Tyne. 



The Carboniferous Limestone series of the north of England con- 

 tains a bed (or beds) of basalt, known as the " Whin Sill," regard- 

 ing the nature of which opinion has long been divided. Some 

 writers regard it as truly interbedded and contemporaneous ; others 

 look upon it as intrusive, and as having been forced laterally between 

 the planes of bedding. The latter opinion is that held by the 

 authors, who stated that through South and Mid Northumberland 

 there can be no doubt as to the intrusive character of the Whin Sill. 

 This conclusion can be established by the line of outcrop of the 

 trap, and also by the evidence of individual sections. 



A review of the literature on the subject was given by the 

 authors, showing that the opinions of geologists are very much 

 divided as to the nature of the Whin Sill. But amongst the prac- 

 tical miners of the north of England there are very few who will 

 admit any doubt that the Whin lies evenly, and at one constant 

 horizon, amongst the strata. Clear cases to the contrary are looked 

 upon as merely local variations, possibly due to successive eruptions 

 of submarine lava. The Whin Sill serves them as a definite line ; 

 and the limestone next above it is always called the " Tyne Bottom 

 Limestone." The question is thus of considerable economic im- 

 portance. It is also of interest in reference to the volcanic history of 

 Britain and to classification. 



Prof. Phillips took the Whin Sill as the base of the Yoredale 

 Series ; the Great Limestone he regarded as its top. But the work 

 of the Geological Survey has shown that the Whin Sill lies at dif- 

 ferent horizons in different places ; sometimes it even lies above the 

 Great Limestone itself. In other words, the Whin Sill, which is 

 supposed to mark the base of the Yoredale Series, sometimes lies above 

 the limestone which forms the top of that series. 



With the disappearance of the supposed base-line of the Yoredales 

 goes also any good reason for drawing a line here at all. The so- 

 called " Tyne Bottom Limestone " cannot be traced definitely through 

 Northumberland ; and the beds above and below this horizon havo 

 the same general character. 



The authors traced the Whin Sill through Northumberland, as far 



