The different forms of implements and weapons which have been treated of in the preceding pages have, for the most part, been fashioned from larger or smaller blocks of stone, reduced into shape by chipping; the chips having apparently been mere waste products, while the block from which they were struck was eventually converted into the tool or weapon required. With the majority, though by no means all, of the Neolithic forms which we still have to pass in review, the reverse holds good; for the raw materials, if I may so term them, from which the bulk of them were made, were flakes or splinters of flint struck off from larger blocks, in such a manner that it was the splinters that were utilized. The block from which they were struck, instead of being the object of the manufacture, became, when all the available flakes had been removed from it, mere refuse, to be thrown away as useless. Before considering any of the various tools and weapons into which these flakes or splinters were converted by subsequent or secondary working, it will be well to say a few words about the simpler forms of flakes, and the cores or _nuclei_ from which they were struck. I have already, in speaking of the manufacture of stone implements, described the manner in which flakes or spalls are, at the present day, struck off by successive blows from the parent block or core, and have suggested the probable methods employed in ancient times for producing similar results. Remarks on the method of production of flint flakes have also been made by Sir W. Wilde,[1158] Sir John Lubbock,[1159] Mr. S. J. Mackie,[1160] Prof. T. McK. Hughes,[1161] and others. I need not, therefore, re-open the subject, |273| though it will be well again to call attention to some of the distinctive marks by which artificially formed flakes may be distinguished from mere splinters of natural origin. The formation of these latter is usually due either to the flint, while still embedded in the chalk, having received some violent shock from disturbance of the stratum; or to unequal expansion, which sometimes causes flints to split up into rudely prismatic forms, much like those assumed by starch in drying, and sometimes causes cracks on the surface, which enable water and frost to complete the work of splitting them. Occasionally, nearly flat planes of fissure are caused by the expansion of some small included particle of a different mineralogical character from the surrounding flint. In such cases a series of concentric and more or less circular rings may usually be traced on the surface surrounding the central particle, which apparently mark the intervals of repose, when its expansion had ceased for a time to exert sufficient force to continue the fissure. This kind of fracture is most prevalent in flints upon or near the surface of the ground, such as those in drift-deposits.