_Growth of continents._ Whatever view as to the general permanence of continents and oceans be ultimately established, the occurrence of widespread changes in the position of land and sea is indisputable, and it is of interest for us to consider the nature of these changes in the formation of continents. Prof. J. D. Dana has put forward a hypothesis of growth of continents by a process of accretion, causing diminution in the oceanic areas, which at the same time became deeper: such growth need not always take place in exactly the same way, and study of the distribution of the strata of the North American continent suggests that the growth there was endogenous, the older rocks lying to the west and north forming a horseshoe shaped continent enclosing a gulf-like prolongation of the Atlantic, which became contracted by deposition and uplift in successive geological periods, though it is still partly existent as the Gulf of Mexico. The Eurasian continent, especially its western portion, suggests more irregular growth around scattered nuclei of older rocks, though the process is not completed, and many gulf-like prolongations, as the Baltic and the Mediterranean, still remain as water-tracts, which have not yet been added to the continents. Although extensive additions to continents may be and no doubt are often largely due to epeirogenic movements, the influence of orogenic movements on continent-formation is very pronounced. As the result of orogenic movements, the rocks of portions of the earth's crust become greatly compressed, and give rise to masses which readily resist denudation; moreover, these comparatively rigid masses, as shown by M. Bertrand, tend to undergo elevation along the same lines as those which formed the axes of previous elevations, and accordingly after a continental area has undergone denudation for a considerable period, the uplands consist of rocks which have undergone orogenic disturbance, while the tracts of ground which are occupied by rocks which have not suffered disturbances of this character, even if originally uplifted far above sea-level, tend to be destroyed, and ultimately occupied by tracts of ocean. Stumps of former mountain chains may be again and again established as nuclei of continents and as every period of orogenic movement will add to the number of these nuclei, the continental areas must in course of time become more complex in structure. Moreover, as some areas are affected by orogenic movements to a greater extent than others, the complexity of different continental masses will vary. Thus, western Europe has been affected by orogenic movements during many periods since the commencement of Cambrian times and its structure is extremely complex, while the central and western parts of Russia have not been subjected to violent orogenic disturbances since Cambrian times, and accordingly we find the structure of that area comparatively simple; the greater part of