65 PART II. <► CHAP. XXIII. Classification of Rocks. The more general facts in Geology having thus been examined, under a separation, which, if not perfect, seems all that a System at present admits, I must proceed to the Second Part of this work, or to de scriptions of the materials which constitute the acces sible earth; though these often entangle enquiries of a general nature. Unfortunately, also, they must often repeat things urged before; because they comprise the Evidences of what has preceded. To produce a System from established materials, is a very simple task: to endeavour to build one out of materials un acknowledged, unknown to others, or controverted, under a perpetual toil through evidences and arguments, is a very different labour: as it is the fate of the writer to pioneer that way which others soon follow; without acknowledgement or effort, yet not without claiming and receiving the praise. But I must premise some remarks on the Classification of these materials; since, besides its practical utility, this constitutes an im portant branch of Geological Philosophy. VOL. II. F