[Sidenote: Limestone and clay] LIMESTONE. Allowing for some districts, like the central plain of Ireland, where the Ice-sheet has left the country very badly drained, a limestone formation usually makes dry soil. The vegetable mould may hold a little water and make mud, as on the chalk downs, but the rock is so porous that most of the rain soaks down, and the waters run mainly underground. Moreover, the vegetable mould gives chemical qualities to this water, which is enabled to dissolve the rocks and form caverns on the underground water courses. At the same time the water becomes 'hard' with lime in solution, so that the springs will petrify moss and twigs. The dryness of the ground tends to make horses sound of bone. The carbonate of lime in the water supplies them with the material for bone. As the result the bones are very light in proportion to their strength. So this pasture registers a well-built and very light horse. If such an animal is of Bay blood, he is larger and swifter than the Arab, lacking only in soundness and in travel endurance. CLAY. As clay holds water, its soils provide abundance to the grass roots, and so produce {40} thick turf with a great weight of green forage to the acre. Such heavy feeding without any exercise in search of water, would, after the killing out of the wolves, tend to produce a large, heavy, slow-going gentle horse with steady nerves such as our draught stock, lacking in that soundness of feet and legs which is limited to the breeds of arid regions. [Sidenote: Horses of Cloudland] So far, the argument presents for the green pastures of cloudland horses of several colours; and, for the varied rock formations in the North Sea and Baltic basins, horses of many types. [Sidenote: Forest varieties] Professor Ewart traces among the ancient wild horses of the forest species three very distinct types: 1. At the time when the glacial drift of the Rhine and Weser valleys had a climate like that of the Outer Hebrides of to-day, the conditions of cold and damp matured the Diluvial horse (Equus Caballus occidentalis). This animal stood fifteen hands, had a longer face than the general forest type, was coarsely built, had heavy fetlocks, a short upright pastern, a broad round foot. This is the cart horse breed. 2. The Grimaldi Grottoes in the Riviera preserve remains of a forest-upland horse, {41} large, coarse, heavy in build, with a short, broad face, and a flat profile. 3. The Solutré Caverns of France preserve paintings made by ancient savages of a small stout, chunky, bearded horse, rather like a long, low Iceland pony, with a short broad face, elk-like nose, and low-set tail, rough-haired towards the root. He stood from twelve to thirteen hands in height. From these three forest varieties our draught horses are mainly descended; but there were also in Ancient Europe two other species besides that of the woodlands.