186 EVIDENCE OP THE FOSSIL FLORA, . 



cellular tissue of the algae is but indifferently suited for pre- 

 servation ; and so it exists as a mere coaly film, scarcely half 

 a line in thickness. 



The most considerable collection of the Lower (Middle) 

 Old Red fucoids which I have yet seen is that of the Rev. 

 Charles Clouston of Sandwick, in Orkney, — a skilful culti- 

 vator of geological science, who has specially directed his 

 palaeontological inquiries on the vegetable remains of the flag- 

 stones of his district, as the department in which most re- 

 mained to be done ; but his numerous specimens only serve 

 to show what a poverty-stricken flora that of the ocean of the 

 Lower (Middle) Old Red Sandstone must have been. I could 

 detect among them but two species of plants, — the one an 

 imperfectly preserved vegetable, more nearly resembling a 

 club-moss than aught else which I have seen, but which bore 

 on its surface, instead of the well-marked scales of the Lyco- 

 podiacece, irregular rows of tubercles, that, when elongated 

 in the profile, as sometimes happens, might be mistaken for 

 minute, ill-defined leaves ; the other, a smooth-stemmed fu- 

 coid, existing on the stone in most cases as a mere film, in 

 which, however, thickly-set longitudinal fibres are occasionally 

 traceable, and which may be always distinguished from the 

 other by its sharp-edged outline, and from the circumstance 

 that its stems continue to retain the same diameter for con- 

 siderable distances, after throwing off at acute angles nume- 

 rous branches nearly as bulky as themselves. In a Thurso 

 specimen, about two feet in length, which I owe to the kind- 

 ness of Mr Dick, there are stems continuous throughout, that, 

 though they ramify in that space into from six to eight 

 branches, are nearly as thick atop as at bottom. They are 

 the remains, in all probability, of a long, flexible weed, that 

 may have somewhat resembled those fucoids of the intertro- 

 pical seas which, streaming slantwise in the tide, rise not un- 

 frequently to the surface in from fifteen to twenty fathoms 



