The deposit, so fruitful in these organisms, has, with much probability, been regarded as a fresh-water limestone, from the circumstance that it contains no corallines or marine shells. The plants, too, are all of a terrestrial or fluviatile kind, and so perfectly entire as to warrant the inference that they have not been tossed and drifted about in an ocean nor transported from a distance, but have perished _in situ_, and dropped amid still waters. It may have been an estuary on the borders of an ancient sea, whither the Megalichthys resembling the crocodile family in bulk, and the Gyracanthi akin to the sharks in voracity, may have roamed in quest of food, gamboled for pleasure amidst a luxuriance of tropical vegetation, or indolently reposed by the umbrageous shades of slimy lagoons. How different the scene over which they maintained undisputed sway from all that is now in these parts subject to man’s dominion. Transpose the zones of the earth, and then only could there be an approximation to the more ancient condition of things. [Illustration: Basin Form of Coal-fields. 1.1. Mountain Limestone.] IV. The Mid Lothian coal-basin is bounded on the west and north-west by the Pentlands, the Braid, and Blackford Hills. The Corstorphine Hills stand out in bold relief above the plain, and are remarkable of their kind; they consist of a sandstone basis, capped by an enormous mass of greenstone, in which the groovings and polish of diluvial or glacial action have long been familiar to the geologist. The carboniferous beds occupy, at intervals, the district toward Falkirk and Stirling, much broken and intersected by the igneous rocks. Stirling, like Edinburgh, is greatly indebted to its physical features, the Abbey-Crag, the dome-shaped and wooded rock of Cragforth, the Castle-Hill, and the Gillies Hill, overlooking and sharing in the glories of the plain of Bannockburn. These all consist of greenstone or dolerite trap, resting on sandstone, or often alternating in nearly conformable beds with sandstone, ironstone, and limestone. The Pentlands stretch about sixteen miles in length by six in their extreme breadth, the axis of the chain bearing almost due N. E. and S. W. The eastern division presents the different varieties of feldspathic rocks—in the center or middle group of hills the graywacke series are more developed—and on the west the old red sandstone and carboniferous deposits prevail. The axis of the chain in some of the higher points is capped with the sedimentary rocks, and along the entire range the phenomena of upheaval, dislocation, subsidence, and denudation all present themselves in turn, and in most instructive forms. The Carlops and Kaim-Valley coal-basin exhibits some remarkable appearances; within a trough-shaped, narrow space, beds of feldspar, porphyry, greenstone, and conglomerate are mixed up with the coal metals, all less or more denuded, separated by transverse openings, and irregularly broken off at their outcrop.