It may here be pointed out that the act of improving upon an invention already existing may be almost wholly a constructive act, performed on a visible and tangible material object, and not on a picture made by the imagination on the mind. In such a case, the act of improving belongs rather in the category of engineering than of invention, for the reason that it involves only a slight use of the imagination. It may also be pointed out, however, that a mere improvement may be, and sometimes has been an invention of the highest order. As a rule, of course, basic inventions have been the most brilliant and also the most important. But it was not only by polished instruments of stone and bone that the New Stone Age was characterized; for we find in the records which our ancestors unintentionally left us, many evidences that they had invented the arts of making pottery, of spinning and weaving, and of constructing houses of a simple kind. This Age was characterized by many improvements besides those relating to articles of stone, and was a period far in advance of its predecessor on the march to civilization. It was marked by the domestication of animals and plants, the tilling of the soil, and a gradual change from a purely savage and nomadic mode of life. This change was first to a pastoral life, in which men lived in fixed habitations and tended their flocks; thence to an agricultural life, in which men cultivated the ground over large areas and grew crops of cereals and vegetables; and then to a still more settled existence, in which men congregated in villages and towns. Certainly, the race had taken the first steps, and had started on the path which it has since pursued. In order to make the start and to proceed afterwards in the line begun, many physical, mental and spiritual attributes were needed and employed, that mere brutes did not possess, and because of which the civilization of the Old Stone Age had been begun and gradually developed. Of these faculties, those principally characteristic seem to have been mental; and among those faculties, invention, reason, construction and memory seem to have been the most important. It would be unreasonable to declare any one of those faculties to have been more important than the others; but it can hardly be denied that the first steps in the march of progress should be credited to invention. Clearly, it was the weapons and utensils of the Old Stone Age that made possible the subduing and subsequent domestication of certain animals, such as the horse, the cow, the dog, the sheep and the goat.