The word "clericus" or "clerk," became synonymous with penman, the sense in which it is still most usually employed. If a man could write, or even read, his knowledge was considered as proof presumptive that he was in holy orders. If kings and great men had occasion to authenticate any document, they subscribed the "sign" of the cross opposite to the place where the "clerk" had written their name. Hence we say, to sign a deed or a letter. Books (MSS.) were extremely rare amongst the Scandinavian and northern nations. Before their communication with the Latin missionaries, wood appears to have been the material upon which their runes were chiefly written: and the verb "write," which is derived from a Teutonic root, signifying to scratch or tear, is one of the testimonies of the usage. Their poems were graven upon small staves or rods, one line upon each face of the rod; and the Old English word "stave," as applied to a stanza, is probably a relic of the practice, which, in the early ages, prevailed in the West. Vellum or parchment afterwards supplied the place of these materials. Real paper, manufactured from the pellicle of the Egyptian reed or papyras, was still used occasionally in Italy, but it was seldom exported to the countries beyond the Alps; and the elaborate preparation of the vellum, upon which much greater care was bestowed than in the modern manufacture, rendered it a costly article; so much so, that a painstaking clerk could find it worth his while to erase the writing of an old book, in order to use the blank pages for another manuscript. The books thus rewritten were called "codices rescripti," or "palimpsests." The evanescent traces of the first layer of characters may occasionally be discerned beneath the more recent text which has been imposed upon them. In Ireland, first known as the Isle of Saints, was founded in the seventh century a great school of learning which included writing and illuminating, which passed to the English by way of the monasteries created by Irish monks in Scotland. Their earliest existing MSS. are said to belong to that period. In the Irish scriptoriums (rooms or cells for writing) of the Benedictine monasteries where they were prepared, so particular were the monks that the scribes were forbidden to use artificial light for fear of injuring the manuscripts. Most interesting and entertaining are the observations of Falconer Madan, a modern scholar of some repute. Of the history of writing in ink during the "Dark Ages" he says: