GYMNOSPERM^. 



103 



NOTES ON THE ADDITIONAL SPECIES OF CONIFERS. 



As already remarked, the Eocene plant-beds were by no means exhausted when the 

 description of the Coniferae was undertaken. On the contrary, greater interest has been 

 aroused, and, in addition to the grant made by the Royal Society, a Committee of the 

 British Association has been formed to continue their exploration. The results of 

 this assistance so far as the Coniferse go are to be found on Plates XV to XXVII, and 

 include many of the most satisfactory and finest specimens. Fresh discoveries have 

 rendered it highly probable that all the Coniferous twigs and leaflets found at Reading 

 and Croydon, though so varied in appearance, may really have belonged to a single 

 dimorphic form of Taxodium, indistinguishable from Glyptostrohus heterophyllus of China 

 and Japan. They could hardly have been placed in one species without such undeniable 

 evidence as that furnished by specimens from Reading, which show the distinct kinds of 

 foliage on the same branch. The abundant specimens of that singular extinct ally of 

 Agathis, Boliostrobus, have been furnished by Mr. E. A'Court Smith, and a visit to Gurnet 

 Bay has enabled me to reproduce the large specimen (Plate XXIII), by means of which, 

 we are enabled to form a satisfactory idea of its habit of growth. But far the most impor- 

 tant additions to our Coniferse, are the fine species of Podocarpus and Ginkgo procured 

 from the Isle of Mull, and which Prof. Newberry and others acknowledge to be the most 

 beautiful fossil remains of these plants ever obtained. They are from a bed from which 

 no collections had previously been made, composed of hard and very fine-grained cement- 

 stone of a pale French-grey and buff" colour, which was not described in detail when 

 the Duke of Argyll referred to it as the lowest of three Leaf-beds, in 1851. The Irish 

 Tertiary Basalts and plant-beds have been described in the preceding pages,^ and it will 

 be of interest to supplement them by an account of those of Scotland.^ 



The Scotch Eocene Basalts. — The position and contour of the beds at Ardtun 

 Head, in Mull, were very fully described by the Duke of Argyll when the occurrence 

 of fossil leaves among the Basalts was first made known. The Head faces Stafili 

 and the Treshnish Isles, which are mere fragments of a once continuous sheet of 

 solid rock that has been cut up and, as it were, dissolved away like so much sugar. 

 As monuments of the resistless power of the waves no scene can be more impressive 

 than this range of scattered islets stretching towards the Atlantic. Most of them 

 appear as horizontal as the slate of a billiard table, and such sheets, extending for 

 miles in every direction, show the overwhelming volume in which the Eocene Basalts 

 must have been discharged. Directly opposite Ardtun, on the other shore of Loch 

 Scridain, is the gigantic headland of Bourg, rising to a height of 1600 feet. This 



1 See p. 77. 



2 They will constantly be referred to in describing the Flora. 



