Prof. G. A. Lehour — Posidonomya BecJieri at Buclle. 75 



limestone. This is a point of much difficulty, owing to the faulted 

 condition of the series in the Bamburgh and Budle district, and more 

 especially to the presence of that disturbing element the G-reat Whin 

 Sill, which there runs in and out among the sedimentary deposits in 

 a very bewildering manner. In 1878, I hazarded the following 

 statement on the subject : — " The interesting fossil Posidonomya 

 Becheri occurs at Budle and in the neighbourhood of Alnwick, and 

 appears to be confined to the Upper Bernician Series. Its exact 

 horizon is doubtful." ^ I am not in a position to add anything to 

 this statement ; but the exact horizon is certainly within the limits of 

 the Bernician, probably in its upper portion, and will be known as 

 soon as the results of my friend Mr. W. Gunn's work on the 

 Government Geological Survey of the district are published. At any 

 rate the beds under discussion are some thousands of feet above the 

 Tuedian. 



The other localities in the North for Posidonomya BecJieri are the 

 Cawledge Burn near Alnwick, where it was found by Mr. Tate ; a 

 small quarry near Denwick (also in the neighbourhood of Alnwick) 

 where Mr. Topley, I believe, first saw it, and where I have myself 

 gathered it ; and lastly at Lowick, where the late Eev. Mr. Jenkinson 

 collected it. All these localities are in the Upper Bernician. 



The range of Posidonomya BecJieri is a subject of great interest. 

 Wherever the Carboniferous Limestone series puts on a shaly facies, 

 there it seems to be present. Many years ago I had the pleasure of 

 seeing specimens of that and another species of the same genus from 

 the shales of Lower Carboniferous age of Western Scotland in the 

 collections of Messrs. James Thomson and Armstrong in Glasgow. 

 Then come the Northumbrian Bernician shales, and next the Devon- 

 shire Culm shales with Posidonomya as described by Dr. Woodward 

 and Mr. J. E. Lee, to the latter of whom I am indebted for beautiful 

 specimens in a shale wonderfully similar in aspect to that of Budle. 

 On the Continent wherever the BergJcalJc gives place to the Kidm — 

 in other words, wherever the Lower Carboniferous sea was shallow 

 and had a muddy instead of a limy bottom, there Posidonomya BecJieri 

 invariably appears, as Dr. Ferd. Roemer and others have so well 

 shown. I have lying before me a little collection of Posidonomyat 

 from Silesia, Nassau, and Portugal due chiefly to Dr. Roemer's kind- 

 ness and including a beautiful specimen quite recently brought from 

 the slaty beds in Southern Spain in which the great Rio Tinto mines 

 are situated, and presented to this College by Mr. David Tyzack. All 

 these specimens, altogether from some fifty places representing a vast 

 extent of country, are absolutely indistinguishable except as to the 

 degree of alteration which the shales containing them have undergone; 

 and the occasional fossils of other kinds which are visible on the slabs 

 are likewise very similar, the presence of long ribbon-like leaves of 

 plants being remarkably general. 



It is perhaps not possible to dogmatize yet as to the limits of the 

 vertical range of Posidonomya BecJieri. I have paid a good deal of 



• ^ Lebour's " Outlines of the Geology of Northumberland," (1878), p. 68. 



