The varieties of tools which have been made out of flakes are too numerous to particularize. Simple flakes, flat or triangular in section, varying in length from nine or ten inches to one inch, are the most abundant of all stone implements, and are to be found in every quarter of the globe. Here they are generally made of flint and are rarely ground. Some of them may have been used as surgical instruments; for, as we shall presently see, trepanning of the human skull was practised in the Neolithic Age.[280] Others were made into saws, the teeth of which are occasionally so fine that to the unaided eye they are hardly visible.[281] Many, shaped like horse-shoes, ducks’ bills, oyster-shells, or short spoons, or nearly round, were used for dressing hides, for scraping haematitic iron ore in order to obtain the red pigment which served primitive man as rouge,[282] and perhaps, in conjunction with nodules of iron pyrites, for producing fire.[283] Some were fashioned into awls and drills;[284] others into knives, daggers, and curved blades, which may perhaps have [Sidenote: Javelin-heads and arrow-heads.] been sickles.[285] But the most beautiful weapons made out of flakes were javelin-heads and arrow-heads, which in this country are almost always of flint. If British neolithic workmanship did not on the whole reach the level of that of Denmark, in fashioning missile weapons our armourers could hold their own. Whether any given specimen was an arrow-head or a javelin-head, a javelin-head or a spear-head, can generally be decided only by size. Many are so small that no one can mistake the purpose for which they were intended; but it is not certain whether the largest were attached to spear-shafts, properly so called, or served as javelins. Arrow-heads and javelin-heads may be grouped in four classes, each of which has several varieties,--leaf-shaped, lozenge-shaped, stemmed, and triangular; but some five or six arrow-heads have been picked up whose outline was characterized by ogee curves. The stemmed heads are generally, and the triangular, which are rare, occasionally barbed. Although the various kinds were used contemporaneously, barbs were perhaps of comparatively late invention,[286] and may have been evolved in the struggle for existence as the population became more dense.[287] Not a single barbed arrow-head or javelin-head has ever been found in a long barrow;[288] but they occur in the chambered cairns of Scotland, as well as in certain English round barrows which were erected towards the end of the Neolithic Age;[289] and a fine specimen was associated with many beautifully finished implements in a neolithic village at West Wickham.[290] A leaf-shaped arrow-head was found in a peat-moss at Fyvie, in Aberdeenshire, still fixed in a cleft in its shaft; but the cord or sinew by which it had doubtless been secured had disappeared.[291] Arrow-heads may also have been made of hardened wood or bone, which holds poison better than flint.[292]