In fig. 13[44] let _A_ represent a shore line of a continent which is undergoing gradual elevation. A deposit of pebbles _a_ will be formed against the coast, one of sand _b_ further away, then one of mud _c_ and lastly limestone _d_, may be formed in the open sea away from land. Naturally there may be intermingling of two kinds of deposit at the junctions, but for the sake of simplicity this may be disregarded. During the accumulation of the deposits _a_, _b_, _c_, _d_, certain sporadic forms may be distributed throughout all the deposits, and some of them may become extinct before the deposition of these beds is completed, if the process is carried out on a large scale; we may speak of the characteristic fossils of this period as fauna I. As the result of elevation or of mere silting up of the sea-margin, or of both combined, the next mass of pebble-deposit will be laid down further away from the original shore, for the shore line will now be at _A´_ and not at _A_, and it will partly overlap the mass of sand _b_; the sand _b_^1 will also be deposited somewhat further out and partly overlap the mud _c_, and similarly the mud _c_^{1} will partly overlie the limestone _d_. During the formation of _a_^{1}, _b_^{1}, _c_^{1}, _d_^{1}, other sporadic forms belonging to a fauna II may replace those of the first fauna. In the same way _a_^{2}, _b_^{2}, _c_^{2}, _d_^{2} will be deposited, and in the meantime a new fauna III may arise and replace II. So the process will go on until we finally have a group of deposits lying one over the other, consisting of a basal accumulation of limestone, succeeded by mud, sandstone and pebble-beds in succession. Each of these will be continuous, though the inner part of the pebble-deposit was formed long before the outer part of the limestone, which is nevertheless beneath a mass of pebble-deposit continuous with that formed first, and the various deposits will be separated by fairly horizontal planes _x_, _y_, _z_, which might be regarded as bedding planes, but which are not so, strictly speaking. The true bedding planes will occur at a slight angle to these planes of separation, for the structure resembles false bedding on a gigantic scale, but of course, the lines separating two masses of similar deposit will be practically horizontal and parallel to the planes of demarcation of two distinct kinds of material. The lines separating two faunas would, under the conditions postulated, run approximately parallel to the planes of separation of adjoining deposits of the same lithological character but would pass from conglomerate, through sandstone, mud and limestone, as indicated by the lines 1, 2, 3, ... and the deposits between adjoining lines would be contemporaneous[45]. In nature, complications will arise, owing to the gradual appearance and disappearance of forms, and the existence of endemic species in contemporaneous deposits formed in different stations and having different lithological characters.