At Hillhead, some distance from Overtown, there is a similar intercalated bed full of hazel remains, and a species of freshwater Ostracoda was detected by Mr. David Robertson.
In a railway cutting a short distance from Beith, Mr. Craig pointed out to my colleague, Mr. Jack, and myself, a thin layer of peaty matter, extending for a considerable distance between an upper and lower mass of till; and at one place we found a piece of oak about four feet in length and about seven or eight inches in thickness. This oak boulder was well polished and striated.
Not far from this place is the famous Crofthead inter-glacial bed, so well known from the description given by Mr. James Geikie and others that I need not here describe it. I had the pleasure of visiting the section twice while it was well exposed, once, in company with Mr. James Geikie, and I do not entertain the shadow of a doubt as to its true inter-glacial character.
In the silt, evidently the mud of an inter-glacial lake, were found the upper portion of the skull of the great extinct ox (Bos primigenius), horns of the Irish elk or deer, and bones of the horse. In the detailed list of the lesser organic remains found in the intercalated peat-bed by Mr. J. A. Mahony,[117] are the following, viz., three species of Desmidaceæ, thirty-one species of Diatomaceæ, eleven species of mosses, nine species of phanerogamous plants, and several species of annelids, crustacea, and insects. This list clearly shows that the inter-glacial period, represented by these remains, was not only mild and warm, but of considerable duration. Mr. David Robertson found in the clay under the peat several species of Ostracoda.
The well-known Kilmaurs bed of peaty matter in which the remains of the mammoth and reindeer were found, has now by the researches of the Geological Survey been proved to be of inter-glacial age.[118]
In Ireland, as shown by Professors Hull and Harkness, the inter-glacial beds, called by them the “manure gravels,” contain numerous fragments of shells indicating a more genial climate than prevailed when the boulder clays lying above and below them were formed.[119]
In Sweden inter-glacial beds of freshwater origin, containing plants, have been met with by Herr Nathorst and also by Herr Holmström.[120]
In North America Mr. Whittlesey describes inter-glacial beds of blue clay enclosing pieces of wood, intercalated with beds of hard pan (till). Professor Newberry found at Germantown, Ohio, an immense bed of peat, from 12 to 20 feet in thickness, underlying, in some places 30 feet, and in other places as much as 80 feet, of till, and overlying drift beds. The uppermost layers of the peat contain undecomposed sphagnous mosses, grasses, and sedges, but in the other portions of the bed abundant fragments of coniferous wood, identified as red cedar (Juniperus virginiana), have been found. Ash, hickory, sycamore, together with grape-vines and beech-leaves, were also met with, and with these the remains of the mastodon and great extinct beaver.[121]
Inter-glacial Beds of England.—Scotland has been so much denuded by the ice sheet with which it was covered during the period of maximum glaciation that little can be learned in this part of the island regarding the early history of the glacial epoch. But in England, and more especially in the south-eastern portion of it, matters are somewhat different. We have, in the Norwich Crag and Chillesford beds, a formation pretty well developed, which is now generally regarded as lying at the base of the Glacial Series. That this formation is of a glacial character is evident from the fact of its containing shells of a northern type, such as Leda lanceolata, Cardium Groènlandicum, Lucina borealis, Cyprina Islandica, Panopæa Norvegica, and Mya truncata. But the glacial character of the formation is more strikingly brought out, as Sir Charles Lyell remarks, by the predominance of such species as Rhynchonella psittacea, Tellina calcarea, Astarte borealis, Scalaria Groènlandica, and Fusus carinatus.
The “Forest Beds.”—Immediately following this in the order of time comes the famous “Forest Bed” of Cromer. This buried forest has been traced for more than forty miles along the coast from Cromer to near Kessengland, and consists of stumps of trees standing erect, attached to their roots, penetrating the original soil in which they grew. Here and in the overlying fluvio-marine beds we have the first evidence of at least a temperate, if not a warm, inter-glacial period. This is evident from the character of the flora and fauna belonging to these beds. Among the trees we have, for example, the Scotch and spruce fir, the yew, the oak, birch, the alder, and the common sloe. There have also been found the white and yellow water-lilies, the pond-weed, and others. Amongst the mammalia have been met with the Elephas meridionalis, also found in the Lower Pliocene beds of the Val d’Arno, near Florence; Elephas antiquus, Hippopotamus major, Rhinoceros Etruscus, the two latter Val d’Arno species, the roebuck, the horse, the stag, the Irish elk, the Cervus Polignacus, found also at Mont Perrier, France, C. verticornis, and C. carnutorum, the latter also found in Pliocene strata of St. Prest, France. In the fluvio-marine series have been found the Cyclas omnica and the Paludina marginata, a species of mollusc still found in the South of France, but no longer inhabiting the British Isles.