Geological Society* 225 



ness. The two systems appear also to be identical in their general 

 character and relations. There are some difficulties arising out of the 

 peculiar modifications of the quartz-rock, which sometimes cannot be 

 distinguished, mineralogically, from that of the unconformable red- 

 sandstone and conglomerate series. The authors have, however, no 

 hesitation in classing the great red-sandstone series, which extends 

 from Applecross to Cape Wrath, with the older portions of the se- 

 condary deposits of Caithness and Sutherland. 



§ 7. Conclusion.— The deposits previously described are here compared 

 with the corresponding formations of England. — 1. The old-red-con- 

 glomerates are, from their mineralogical character and position, iden- 

 tified with the old-red-sandstone of English geologists. — 2. The great 

 central deposit, containing the ichthyolites, does not appear to be 

 perfectly identical with any formation hitherto described. It seems 

 in some measure to occupy the place of the coal-formation. Many 

 parts of it resemble grauwacke in mineralogical character j and from 

 its enormous development, it can hardly be compared with the cop- 

 per-slate of Germany. Again, none of the fish of Caithness are iden- 

 tical with the fish of the copper-slate. The upper part of the Caith- 

 ness schist might however, in accordance with the Arran section, be 

 compared with the copper-slate ; in which case the red-sandstone of the 

 Pentland Firth might be considered as the representative of the new- 

 red-sandstone of England. There is however a break in the series, 

 and it is perhaps impossible to determine where the interruption takes 

 place.— 3. The red-sandstone on the shores of the Pentland Firth 

 most nearly resembles the red-sandstone of Arran, which is interposed 

 between the coal measures and the conglomerates of the new-red- 

 sandstone. 



A paper was read by the Rev. Dr. Buckland, on the Cycadeoidea, 

 a new family of fossil plants, specimens of which occur silicified in the 

 Free-stone quarries of the Isle of Portland. 



These fossils have as yet been noticed only in the Isle of Portland ; 

 their existence has long been known to many persons, and to the au- 

 thor, who acknowledges the assistance of Mr. Brown and Mr. Lod- 

 diges, in assigning to them their place in the vegetable kingdom, 

 where they stand near the living Genera Zamia and Cycas. 



Their external form approaches to that of the fruit of a pine-apple, 

 and is still more like the trunk of a living Zamia, varying from five to 

 fifteen inches in height, and from eight to fifteen inches in width. The 

 stems are nearly cylindrical, and terminate downwards in abroad flat 

 bottom, without any indication of roots : they have no true bark, but 

 are inclosed in a thick case, composed of the permanent bases of de- 

 cayed leaves, having a structure like that of the bases of the leaves of 

 the recent Zamia; they are terminated externally by lozenge-shaped 

 impressions, or scars, of which a continuous series winds spirally, like 

 the scales on a fir-cone, round the whole exterior of the plant. 



As yet no leaves have been found adherent to any of these fossils, 

 but at the upper end there is a cavity, from which the crown and last 

 leaves appear to have been removed, before the petrifaction of the 

 stems. 



New Series. Vol. 4. No. 2 1 . Sept. 1 828. 2 G The 



