We cross the beach, and enter on a bare brown moor, comparatively fertile, however, in the club mosses. One of the largest and finest of the species, _Lycopodium clavatum_, with its long scaly stems and upright spikes of lighter green,--altogether a graceful though flowerless plant, which the herd-boy learns to select from among its fellows, and to bind round his cap,--goes trailing on the drier spots for many feet over the soil; while at the edge of trickling runnel or marshy hollow, a smaller and less hardy species, _Lycopodium inundatum_, takes its place. The marshes themselves bristle thick with the deep green horse tail, _Equisetum fluviatile_, with its fluted stem and verticillate series of linear brandies. Two other species of the same genus, _Equisetum sylvaticum_ and _Equisetum arvense_, flourish on the drier parts of the moor, blent with two species of minute ferns, the moonwort and the adder's tongue,--ferns that, like the magnificent royal fern (_Osmunda regalis_), though on a much humbler scale, bear their seed cases on independent stems, and were much sought after of old for imaginary virtues, which the modern schools of medicine refuse to recognize. Higher up the moor, ferns of ampler size occur, and what seems to be rushes, which bear atop conglobate panicles on their smooth leafless stems; but at its lower edge little else appears than the higher Acrogens,--ferns and their allies. There occurs, however, just beyond the first group of club mosses,--a remarkable exception in a solitary pine,--the advance guard of one of the ancient forests of the country, which may be seen far in the background, clothing with its shaggy covering of deep green the lower hill-slopes. And as we found in the Thallogens of that littoral zone over which we have just passed, representatives of the marine flora of the Silurian System, from the first appearance of organisms in its nether beds, to its bone-bed of the Upper Ludlow rocks, in which the Lycopodites first appear, so in the Acrogens of that moor, with its solitary coniferous tree, we may recognize an equally striking representative of the terrestrial flora which existed during the deposition of these Ludlow rocks, and of the various formations of the Old Red Sandstone, Lower, Middle, and Upper. [Illustration: Fig. 10. PINUS SYLVESTRIS. (Scotch Fir.)] [Illustration: Fig. 11. CALAMITE? Of the Lower Old Red Sandstone. Shetland. (One eighth nat. size.)] [Illustration: Fig. 12. LYCOPODITE? Of the Lower Old Red Sandstone. Thurso. (Mag. two diameters.)]