In the preceding classes of irregular coasts the bays are, after all, of comparatively small dimensions, and the general trend of the coast is not greatly affected by them, but there are other coasts, where the land is invaded by very broad, deep gulfs, which are not mere indentations, and the interlocking gulfs and peninsulas are of the same order of magnitude. Greece is a typical instance of the lobate coast, and the islands of Celebes, Japan, and Haiti are other examples of the same type. The origin of the gulfs, which are usually very deep, is probably to be ascribed to faulting.

Professor Penck has calculated that, in round numbers, 37% of the sea-coasts of the earth belong to one or other of the irregular types; and of this amount nearly one-third is of the fjord coast class and rather less than half of the rias coast class. Of the continental coasts 43 % are regular, and two-thirds of these are low, flat coasts, and nearly one-third adjusted. As the flat coasts are due to accumulation and many of them to upheaval, but a small amount remains as directly formed by wave erosion. From these figures it appears that diastrophism is of more importance than marine denudation in determining the character of the coast-lines.