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valley of Swan Creek southeast across sec. 5, T. 120 N., R. 76 W., a branch of Little Cheyenne. Its sides were studded with bowlders, which rose somewhat higher than the surrounding country and which by erosion in places were made to resemble hills or osars.

The Ree Valley loop differs from most that we have considered, in that the region outside and within the moraine is on about the same level. This is particularly true to the west and south. The plain within this loop is considerably more even than in other loops that we have described. Its general altitude may be inferred from some preliminary railroad surveys, which show that 8 miles south of Gettysburg it is 1,960 feet above the sea. Near the northeastern corner of T. 116 N., R. 78 W., it is 1,840 feet. Toward the south it is some. what lower, being about 1,700 feet northwest of Blunt and about the same distance northeast of Pierre.

THE REE HILLS.

East of the hills south of Blunt is a broad valley 4 or 5 miles wide. Beginning about 3 miles south of Blunt and rapidly deepening it extends to the main bowldery terrace of the Missouri, with which it is continuous. Along the western side of this valley lies another terrace with the higher gravelly knolls along its western side. This is shown in Pl. XX. The inner or eastern edge of the terrace is about 400 feet above the Missouri River. Rising from the east side of this valley, near the north line of T. 111 N., R. 74 W., is found the Outer moraine, 3 to 5 miles in width, which runs directly eastward, gradually rising. It presents the appearance of clustered knolls and basins, which are not prominent in the Ree Valley loop. Its southern slope is drained along its western half by Chapelle Creek, and its eastern half drains into the north branches of Crow Creek, especially the Boxelder, which heads in the internal drainage system of the eastern end. The Second moraine joins the First near the west line of Hand County and skirts the whole circumference of the high eastern end of the Ree Hills. It is generally separated from the First moraine by a valley with ponds. Two interesting peculiarities may be noted of the Ree Hills. The first, which is the most striking, is the fact that the ice seems to have broken through the ridge at its eastern end so as to reach the main internal drainage channel, which extended toward the south, making the subglacial plain continuous with the high terrace along Boxelder Creek. The other is the elaborate drainage system found at the east end of the hills. From a gap about a mile and a half southwest of Ree Heights and 150 feet above that station the channel begins, and, with widenings natural to such features, runs nearly directly southward for 8 or 9 miles. It receives from the west and southwest three or four tributaries, from the east about as many more, but smaller. About 5 miles from Ree Heights, where it receives two large tributaries from the southwest, its bottom is about 90 feet above the station

of Ree Heights and three-fourths of a mile wide. Its sides are 60 to 70 feet in height, abrupt, and very stony. Occasional mounds of gravel are found in the channel. The highest point of the Ree Hills is about 300 feet above the station, or about 2,050 feet above the sea. South of Highmore it is about 2,000 feet, and south of Holabird a little lower.

The Ree Hills are probably largely composed of Cretaceous clays in situ. About 6 miles south of Ree Heights a whitish "soapstone" or clay was found within 100 feet of the highest point of the hills, and farther south in a prominent bluff this was less distinctly traced considerably higher. The hills lie along the northern edge of the tableland which ends in an abrupt edge looking south. This front extends east and west about 12 miles and about that distance south of the Chicago and Northwestern Railroad. This bluff seems to have been formed by the erosion of numerous branches of Boxelder Creek, which have removed quite rapidly the Cretaceous clays. South of the western half of the moraine the country was examined to the great bend of the Missouri, and found to present erosive topography, but with a fine veneering of drift, in which bowlders were abundant, especially at certain points. It was thought that the northern side of the hills exhibited more bowlders than the southern, and in Pl. IX a view is given of one of the most striking hillsides of this sort. Seen from the outside, it might be mistaken for a morainic hill, but an examination showed that erosion had developed in its front a crater-like basin, which is shown in Pl. X. This basin exhibited Cretaceous clays along its inner side and was clearly the result of erosion. Moreover, the arrangement of these hills forbids the idea of their morainic origin. Artificial excavations not being found in the region, the depth of the drift can only be inferred.

THE BOXELDER LOOP.

This is in some respects the most perplexing and least satisfactorily explained portion of the moraine. The position of the morainic hills may be described as follows: South of a gap about 3 miles in width, which has been alluded to under the last heading, morainic hills begin on the east side of Boxelder Creek, near the south line of T. 110 N., R. 70 W., in the southwest corner of Hand County, and continue in a southerly and southeasterly direction along the eastern side of the valley of that stream, forming the watershed between it and the next branch of Crow Creek to the east. A slight reentrant angle heading toward the northeast is formed in the northern part of T. 107 N., R. 69 W. With this irregularity it continues directly to Crow Creek, near the eastern line of Buffalo County, south of Gann Valley. Thence eastward, where it is much less distinctly developed, consisting mainly of scattered knoll ridges, rarely over 15 feet in height, nearly 12 miles, when it turns northward and soon joins a high, irregularly triangular area covering the most of T. 108 N., R. 66 W. At its northwestern angle