410 Ward — Geology of the Little Colorado Valley. 



that they have to be regarded as virtually overlying the con- 

 glomerates. In fact, in the bed of the Moencopie Wash, on 

 both sides of which these beds are so well developed, the con- 

 glomerates can be seen distinctly passing under the marls. 



So much for the variegated marls, which, for the purposes of 

 our expedition, constituted the most important subdivision of 

 the entire. formation. But as we have seen, their maximum 

 thickness is about 400 feet and there remain still another 

 400 feet before we reach the base of the painted cliffs. 

 Throughout the whole of this fossil wood is abundant, but the 

 character of the beds as variegated marls no longer continues. 

 In the lower Colorado Valley, where I know it best, the varie- 

 gated marls are succeeded by a sandstone ledge at least 100. 

 feet in height, yielding black logs of very fine structure. At 

 this point these sandstone beds constitute an escarpment and 

 form a small terrace, the summit of which is a dip plane. 

 Upon this lie the remains of the next set of beds, which are 

 somewhat remarkable, primarily in being essentially limestones, 

 but they consist mainly of loose material somewhat resembling 

 dried mortar, for which reason I have designated them mortar 

 beds. They are, however, very irregular in structure and contain 

 much impure flint and large flinty stones. In the midst of them 

 there occurs a true limestone ledge, well stratified, succeeded 

 by a continuation of the mortar beds. In the region mentioned 

 these beds extend to the limit of what 1 regard as true Shina- 

 rump, and petrified wood was found above the limestone ledge. 



A wider acquaintance with this part of the formation shows 

 that the conditions above described do not hold at all points 

 and may even be regarded as exceptional. Nowhere else 

 except at Black Falls did I find the lower sandstone ledge, and 

 at most other points the limestones gradually supervene upon 

 the variegated marls. In fact, it should be remarked, that not 

 only the variegated marls but also the shales of the conglomerate 

 series, which become transformed into marls, are more or less 

 calcareous ; and when we find that the entire upper portion of 

 the Shinarump consists mainly of limestones and calcareous 

 materials, we may regard all of this, including the variegated 

 marls, as virtually a calcareous deposit. If we were to look 

 abroad for its homologue in the Trias of the Old World we 

 would find it in the Muschelkalk, while the conglomerate series 

 might well be compared with the Buntersandstein, and the 

 Painted Desert beds with the Keuper, to which the French term 

 Marnes Irisees is only locally applicable. 



In the extensive exposures on Le Roux Wash these relations 

 are brought out with great force. Overlying the true varie- 

 gated marls which stretch out for a distance of three miles 

 across the broad eroded valley, the limestone series comes in grad- 

 ually and scarcely differs except in the degree of calcareousness 



