Below the rocky cliffs which line the valley sides are boulders brought by the ice from near-by ledges, and about one-half mile above the head of the swamp are remnants of a terrace standing 20 to 30 feet above the level of the stream. Although the terrace appears to consist of till, it may conceal a rock floor which was cut by a former stream. As the valley is followed toward Neversink Pond, the various features of a till-coated, rock-floored valley are seen. [Illustration: ~Fig. 6.~ Course of Still River. Dotted lines show the preglacial channels.] STILL RIVER STATEMENT OF THE PROBLEM Still River presents several unusual features, as shown in fig. 6. Tributaries from the west and south unite at Danbury to form a stream flowing northward opposite to the regional land slope. Near its junction with the Housatonic, the river flows northward, whereas its master stream half a mile distant flows southward. The lower valley of the river is broad and flat and apparently much out of proportion to the present stream; it is, indeed, comformable in size and direction with the valley of the Housatonic above the mouth of the Still. The Housatonic, however, instead of choosing the broad lowland in the limestone formation, spread invitingly before it, turns aside and flows through a narrow gorge cut in resistant gneiss, schist, and igneous intrusives. The headwaters of the Still mingle with those of the Croton system, and its chief southern branch, the Umpog, is interlaced with the sources of the Saugatuck on a divide marked by glacial drift and swamps. The explanation of these features involves not only the history of the Still River system, but also that of the Housatonic. In explanation of the present unusual arrangement of streams in the Still River system, four hypotheses may be considered: I. Still River valley is the ancient bed of the Housatonic from which that river has been diverted through reversal caused by a glacial dam. II. The Housatonic has always had its present southeasterly course, but the Still, heading at some point in its valley north of Danbury, flowed initially southward through one of four possible outlets. The latter stream was later reversed by a glacial dam at the southern end, or by glacial scouring at the northern end of its valley which removed the divide between its headwaters and the Housatonic. III. The Housatonic has always held its present southeasterly course, and the Still initially flowed southward, as stated above. Reversal in this case, however, occurred in a very early stage in the development of the drainage, as the result of the capture of the headwaters of the Still by a small tributary of the Housatonic. IV. The Housatonic has always held its present southeasterly course, but the Still has developed from the beginning as a subsequent stream in the direction in which it now flows.