| PERIODS | ||||
|---|---|---|---|---|
| RECENT | ||||
| PLEISTOCENE | ||||
| PLIOCENE | ||||
| MIOCENE | ||||
| OLIGOCENE | ||||
| EOCENE | ||||
| CRETACEOUS | THICKNESS | |||
| SOFT SANDSTONES GRITS & CLAYS | DENVER & ARAPAHOE | 2000 ft. | ||
| SANDSTONES, SHALES & LIGNITE | LARAMIE | 1000 ft. | ||
| YELLOWISH SANDS & SHALES | FOX HILLS | 1000 ft. | ||
| SOFT DARK GRAY OR RUSTY SHALE | PIERRE | 5000 ft. | ||
| LIMESTONES & SHALES | NIOBRARA | 500 ft. | ||
| DARK SHALES & LIME | BENTON | 400 ft. | ||
| GRAY OR BUFF SANDSTONES & CLAYS | DAKOTA | 300 ft. | ||
| SHALES, SANDSTONE & LIME | MORRISON | 200 ft. | ||
| JURASSIC | ||||
| TRIASSIC | ||||
| PERMIAN | ||||
| DEEP-RED SANDY SHALES, LIME, GYPSUM | LYKINS | 700 ft. | ||
| CARBONIFEROUS | ||||
| MASSIVE PINK OR WHITE SANDSTONE | LYONS | 200 ft. | ||
| RED OR BROWN SANDSTONE & CONGLOMERATE | FOUNTAIN | 1500 ft. | ||
| DEVONIAN | ||||
| SILURIAN | ||||
| ORDOVICIAN | ||||
| CAMBRIAN | ||||
| PRE-CAMBRIAN | ||||
| METAMORPHIC & INTRUDED ROCKS SCHIST, GNEISS, QUARTZITE | IDAHO SPRINGS (PART) | |||
| BASEMENT ROCKS of IGNEOUS ORIGIN |
A generalized section for the western part of the Denver Basin is introduced here for the use of local students. The formations normally present in this region are shown in their usual position. They are briefly described on the chart, and their thickness is indicated by figures which may be regarded as near the maximum for the district. The section will apply to most of the foothills area between Morrison and Boulder though surface features and thickness of beds will vary considerably from place to place.
Certain of the formations are known to be fossil bearing, others barren or nearly so. When fossils are present they are usually restricted to certain localities, and these may be widely scattered. The following remarks apply to the possibilities for finding fossils in the formations named.
Denver and Arapahoe.
Leaf impressions of palms, ferns, and numerous species of well-known trees and shrubs are common in many localities. Petrified wood is fairly abundant, and a few scattered bones of reptiles and mammals have been found. The two formations are treated as a unit because the Arapahoe is neither conspicuous nor sharply defined. Denver beds are well exposed on the slopes of Table Mountain at Golden; fossils, however, have been obtained from several localities nearer the city of Denver, notably from the hills just west of Overland Park.
Laramie.
Plant material is locally abundant, principally the leaves of familiar deciduous trees, palms, and ferns. Many of the clay pits being worked near Golden are in this formation. Oysters and a few other mollusks may be found in some places.
Fox Hills.
Better exposures of this formation are located to the north of Denver. Marine mollusks are most frequently found.