THE BASALTS OF IRELAND AND SCOTLAND. G57 



Islands, and us far north, as Japan." The frond seems to have 

 heen dichotomous, for fig. 5 appears to represent parts of two 

 basal pinna?, while 6 may be a terminal one. 



A species belonging to tho same section of Gleichenia, with 

 very similar pinna?, occurs in the Middle Eocene of Bournemouth, 

 but is distinguished by the conversion of some of its pinna? into 

 hook-like tendrils, differing from those of any existing fern. No 

 other Tertiary fossil species at all resembles it except one from 

 tl.e very ancient Eocene of Sezanne; but similar species existed 

 in the late Cretaceous of Aix-la-Chapelle. The Bournemouth 

 species is almost limited to a small patch, only a few yards in 

 extent ; but the Irish species seems to have been spread rather 

 widely, having already been found at two localities many miles 

 apart. These seem, however, to have been near its northern 

 limits, for it has never been found among the numerous fossil 

 floras met with in this basaltic formation nearer to Arctic 

 regions. 



The genus Gleichenia seems to have reached its culminating 

 development in Europe in Cretaceous times, and thenceforward 

 to have rapidly disappeared. 



The likeness between the fossil and its living representative 

 falls short of specific identity. So vast an interval has elapsed 

 that the marvel is that the growth and venation of any fern should 

 have continued, while all else around it has progressed, without 

 modificatiou. "We have examples of such, however, in Chry sodium 

 vulgare, Osmunda javanica, Onoclea sensihilis. Other Eocene 

 species are only separated from their living allies by trifling cha- 

 racters : among these is the Gleichenia like G. dichotoma, but 

 with a climbing habit, and close allies of Pteris cretica and Lygo- 

 dium palmatum, a Phymatodes, and an Adiantum. In the latter 

 category must the Irish G. hibernica be placed ; though at any 

 moment specimens gathered from a fresh locality may show 

 a closer agreement, amounting, perhaps, to identity, absolute and 

 complete. 



No other Tertiary fossil can readily be confounded with it. 

 The few specimens I possess from Glenarm were found close to- 

 gether during my last day's work there. Mr. Stewart obtained 

 a specimen from Ballypalady in which only the rhachis and mid- 

 ribs remained distinct, and I possess another in the same matrix 

 in which some of the veinlets are faintly discernible. 



