It has often happened to geologists, as to other explorers of new regions, that footprints on the sand have guided them to the inhabitants of unknown lands, and such footprints, proverbially perishable, may be so preserved by being filled up with matter deposited in them as to endure for ever. This we may see to-day in the tracks of sandpipers and marks of rain-drops preserved in the layers of alluvial mud deposited by the tides of the Bay of Fundy, and which, if baked or hardened by pressure, might become imperishable, like the inscriptions of the old Chaldeans on their tablets of baked clay. The first trace ever observed of reptiles in the Carboniferous system consisted of a series of small but well-marked footprints found by Sir W. E. Logan, in 1841, in the lower coal measures of Horton Bluff, in Nova Scotia; and as the authors of most of our general works on geology have hitherto, in so far as I am aware, failed to do justice to this discovery, I shall notice it here in detail. In the year above mentioned, Sir William, then Mr. Logan, examined the coal fields of Pennsylvania and Nova Scotia, with the view of studying their structure, and extending the application of the discoveries as to beds with roots, or Stigmaria underclays, which he had made in the Welsh coal fields. On his return to England he read a paper on these subjects before the Geological Society of London, in which he noticed the subject of reptilian footprints at Horton Bluff. The specimen was exhibited at the meeting of the Society, and was, I believe, admitted, on the high authority of Prof. Owen, to be probably reptilian. Unfortunately Sir William's paper appeared only in abstract in the Transactions; and in this abstract, though the footprints are mentioned, no opinion is expressed as to their nature. Sir William's own opinion is thus stated in a letter to me, dated June, 1843, when he was on his way to Canada, to commence the survey which has since developed so astonishing a mass of geological facts. [Illustration: Footprints of _Hylopus Logani_, Dawson, Lower Carboniferous, Nova Scotia. Natural size and reduced. These footprints were the first indications of Carboniferous land vertebrates ever observed; they were probably made by a Microsaurian and one of the earliest species of this type. They show a remarkable length of stride and development of limb.]