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THE CRETACEOUS RIM OF THE BLACK HILLS.
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course and opens into the Minnekahta Valley. The locality is on the southeast slope, just below the top of the flat-topped spur-ridge and near the abrupt descent into the cañon. From this point northwest to near the crest of the divide the slope is moderate and nearly uniform.

The accompanying sketch-map (Fig. 2) showing the drainage of the region north of the south fork of the Cheyenne river, the Minnekahta Valley, and part of the Red Valley, will enable the reader to understand the general character of the country covered by this reconnaissance.

Fig. 2.Sketch-map of a portion of Fall River County, South Dakota.

A B.Section No. I.

  1. Cycad bed.
  2. Fossil forest.
  3. Plant bed.

C D.Section No. II.

  1. Upper leaf bed.
  2. Lower leaf bed.

At the foot of this crest on the same (southeast) side, and about one and a half miles northwest of the cycad locality, occurs an extensive fossil forest. The wood is all completely silicified, and consists of prostrate trunks of various sizes and lengths and an abundance of smaller fragments, many of which are scattered about on the sloping plain a long distance below the actual horizon at which they were petrified. At that horizon many still remained apparently undisturbed, and on one place a trunk eight inches in diameter was seen projecting several feet from beneath the massive sandstone ledge. To the south of this point is a

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