It remained to find a better fulcrum than that afforded by the rough turf over which such logs, when burdened, were rolled. What probably followed is well described by Bridges Adams.[2] “The next process,” he thinks, “would naturally be that of cutting a hole through the roller in which to insert the lever. The convenience of several holes in the circumference of the roller would then become apparent, and there would be formed an embryo wheel nave. It could not fail to be remarked also, that the larger the roller, the greater the facility for turning it, and consequently the greater the load that could be borne upon it.” Owing to the difficulty of using such large logs, he goes on to suggest, a time would come when it was found that a roller need not bear upon the ground throughout its length, but only at its extremities. So from the single roller would be evolved two rough wheels joined by a beam, square at first though afterwards rounded, upon which could be fixed a frame for the load. Such axle and wheels would revolve together and keep the required position by means of pieces of wood which may be compared with the thole-pins of a boat. And it is a remarkable fact that until last century such primitive carts were in use in Portugal and parts of South America. The chief drawback to a vehicle of this kind is its inability to turn in a small space, and the pioneers, whoever they were, finally discovered the principle of the fixed axle-tree, the wheels revolving upon their own centre. So, “instead of fixing the cross-beam or axle in a square hole,” these pioneers “would contrive it to play easily in a round one of a conical form, that being the easiest form of adjustment.” Such a car as this, with solid wheels and a rude frame, was used by the Romans, and is still to be seen in parts of Chili. The next process in the evolution of the wheel doubtless followed upon the necessity of economising with large sections of wood, and there was finally invented a wheel made of three portions—a central pierced part, the nave, an outside circular piece, the rim or felloe, and two or more cross-pieces, joining the two, the spokes. Of these the felloes would tend to wear soonest, and a double set would be applied to the spokes, as was the case until recently in the ox-carts of the Pampas, or _barcos de tierra_, as they were called by the natives. And indeed, the first carriages of which we have particular information, the chariots of the Egyptians and their neighbours, differ essentially from such primitive carts only in the delicacy and ornamentation of the carriage body. [Illustration: _Types of Primitive Carts_]