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Colorado Springs , they form a perfect and imperceptible transition fromthe Sandstone No. 3, downward to undisputed Cretaceous . With possi-bly one exception, the Lignitic and Cretaceous series are everywhere per-fectly conformable. Mr. Marvine found distinct unconformability betweenthem in Middle Park near Mt. Bross ; but this must be quite local, forDr. Ilayden states respecting Middle Park, in the same vicinity,that theTertiary rocks are found in great thickness and perfectly conformable tothe underlying Cretaceous . At many localities east from the mountainsa conglomerate occurs resting unconformably upon the lignitic rocks.
About twenty miles south from Cheyenne, this group is exposed. TheCretaceous passes up imperceptibly into the fucoidal sandstone, which isninety-five feet thick. At a few feet above the sandstone is a coal-bed,four to six feet thick, roofed by clay, containing an oyster like 0. subiri-gonalis. On Boulder Creek, the same Ostrea is found above the coal.Near Golden, the sandstone is separated from the Cretaceous beds byonly a few inches of clay, and contains dicotyledonous leaves alongwith Halymenites major. Near Colorado Springs this rock contains aa variable seam of coal, and affords the fucoid and dicotyledonous leaves.Below it are layers of clay and shale, yielding Baculiten with other Cre-taceous forms, and passing downward into Cretaceous dark shales.
In the vicinity of Canon City, on the Arkansas , the succession is clearlyshown. The dark Cretaceous shales gradually merge into a mass ofclay and argillaceous sandstones which passes upward imperceptibly intothe fucoidal sandstone. In the upper portion of this loose-grained rockthere are many impressions of fucoids and, in some of the more compactlayers, indefinite impressions of mollusca. In the upper portion of theclay-beds Dr. Hayden found an imperfect Inoeeramus. Prom this localitysouthward, the sandstone is easily followed, standing out like a wall forlong distances. Near Trinidad, on the Purgatory River, Mr. Lesquereuxfound it 200 feet thick, resting on the dark shales of the Middle Creta-ceous. On Raton Creek it is 178 feet, resting on the Cretaceous shales,and overlaid by 300 feet of coal-bearing rocks. On Vermejo Creek, thesandstone contains three thin seams of coal. At Canon City it containscertainly two.
Respecting the relations of the Cretaceous and the Lignitic Group, eastfrom the mountains, Dr. Hayden says, “These black shales pass gradu-ally up into rusty arenaceous clays, which characterize No. 5 ; and No. 5passes up into the Lignite Tertiary beds, where they can be seen in con-tact, without any well-defined line of separation that I could ever dis-cover.”*
In its southern extension and near the mountains the fucoidal sand-stone is for the most part of a texture unfavorable to the preservation oforganic remains and seldom contains any other than very rude specimensof fucoids. Dr. Hayden states, that he has searched it over an area ofmany miles, but has succeeded in finding no fossils excepting “one* Reprint of Reports, p. 121.