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MORRISON SHALES OF COLORADO AND NEW MEXICO 55 
leaves little room for doubt that they are two distinct forma- 
tions. A similar contrast is apparent in the canyon of the 
Canadian and the exposures along the mountain front. There 
is little doubt, therefore, that the shales are separate and distinct 
irom the Red Beds: 
Wherever the shale formation was found in this region its 
character is the same. Minor variations occur constantly within 
the formation, which in themselves constitute one of its most 
persistent features. The clay-shales vary laterally, as well as 
vertically, through arenaceous shales to sandstone on the one 
hand and through calcareous shales to pure limestone on the 
other. The members of the formation, however, are in general 
easily distinguished from the Dakota above and from the Red 
Beds beneath. There are wide areas within the region in which 
the shales are not exposed. But their lithological character 
wherever seen leads to the inference that throughout the region 
examined the shale series is one and the same formation. 
The age of the formations underlying the shales is not defi- 
nitely known. The Red Beds along the base of the mountains 
have been called Triassic by many geologists, while some por- 
tions at least have been referred to the Carboniferous by others. 
The Red Beds of the Purgatory Canyon seem to differ in no 
essential manner from those near the mountains, unless it be in 
the greater massiveness of the upper series—the upper 100 to 
200 feet of the Purgatory Red Beds being massive sandstone. 
The Red Beds of the upper Rio Cimarron seem to be indentical 
with those of the Purgatory and the mountain front. Those of 
the lower Rio Cimarron are less massive, and composed of thin 
seams of red sandstone interstratified with red to purple shales. 
In this respect they resemble the lower series of the Red Beds 
exposed in the Purgatory.*. The unconformity at the summit of 
this series indicates that the upper portion of the Red Beds has 
been removed. The Exeter sandstone entering from the east 
or south and thinning towards the west lies unconformably upon 
the Red Beds. The Red Beds of the Canadian, with the excep- 
' LEE, JouR. GEOL, Vol. IX, No. 4, May-June, 1901, Sec. I, p. 346. 
