With the data already gathered, we can not escape from the conclusion that the growth going on at the head of the lake will in time, if present conditions continue to exist, push its way forward until it has occupied the whole water area. The sediment which is now deposited therein will then be transported across the plain, and will be carried along until another body of water is reached. Further search will bring to light the fact that there are plenty of examples showing all stages between the simple delta and the completely filled lake. The innumerable marshes and meadows which characterize the northern part of the United States are fine examples of lakes which have perished in this manner. [Illustration: FIG. 4.--A COMMON FORM OF LARGE DELTA.] Our next excursion will be made to the locality shown in Fig. 4, which is a sketch of a large delta occurring at a considerable height above the general level of the country, although at the present time the delta is not in vicinity of water.[10] It will be evident to the reader that it differs in no important particular, excepting size, from our little type specimen formed in a pool. Its level top and frontal lobes are to-day nearly as strongly marked as at the time it was made. The reader will have little difficulty in picturing the original conditions of its formation in some ancient lake. This old lake did not endure until the inflowing streams had filled it to a level plain, but for some reason, which it is unnecessary for us to consider, the water was permitted to escape, leaving the delta perched on the valley side. Such deltas are very common, and we find them in all stages, from simple beginnings, as above, to the completed sand plain. [Illustration: FIG. 5.--GEOLOGICAL CROSS-SECTION OF A DELTA.]