LABAMIE PLAINS. 83 



texture, and seem highly arenaceous throughout most of the beds. Of the 

 Mesozoic strata, the Red Beds, Jurassic, and Dakota Cretaceous lie inclined 

 from 20° to 30°. Here the bluish-drab, clierty limestone of the Jurassic 

 forms a prominent outcrop, rising slightly above the enclosing marls. Over- 

 lying the Dakota Cretaceous, the clays of the Colorado group incline at a 

 gentler angle, affording few exposures, except the two low rolls of blue and 

 yellow marls in the Niobrara division. Except in the latter beds, no organic 

 remains were found in the entire series, and these were confined to the genus 

 Ostrea. The Fort Pierre black clays dip away from the Niobrara beds with 

 a slight angle, soon becoming nearly horizontal, and, so far as visited, appear 

 to occupy the greater part of the circular basin north and west of Bellevue 

 Peak, through which the numerous tributaries of the Little Laramie River 

 run, and as these streams cut but little into the clays, their banks offer poor 

 exposures of strata. It is possible that at the upper end of the basin older 

 rocks than Cretaceous may be exposed resting against the Archsean range. 

 The surface of the basin is quite level, and furnishes excellent grazing-land 

 for large herds of cattle. 



Along the broad valleys of the Big and Little Laramie River, and, 

 indeed, over the greater part of the plains, long bench-like ridges form a 

 characteristic feature of the region. p]xcept on their edges, the benches 

 present but few outcrops, and these usually exhibit coarse sandstone beds, 

 lying in a nearly horizontal position. In numerous localities, organic 

 remains have been found embedded in the sandstones, and have in every 

 case been sufficiently characteristic to show that the beds belong to the 

 Colorado group, without clearly determining the more limited subdivisions 

 of the series. It seems evident, therefore, from our explorations, that the 

 central portion of the Laramie Plains is underlaid by the Colorado group, 

 and that all the beds may be present, but with more or less of an arena- 

 ceous texture. At the northern end of the plains, between Lake lone and 

 the Laramie River, in a yellowish-brown sandstone, was found the charac- 

 teristic Fort Pierre species, Baculites ovatus, their surfaces being coated with 

 exceedingly beautiful iridescent hues, associated with the genus Ammonites. 

 At the southern end of the plains, near where the Laramie River crosses 

 the western boundary of the Fort Sanders military reservation, the banks 



