26 MESOZOIC FLORAS OF UNITED STATES. 



another 400 feet l^efore we reach the base of the pamted chffs. Through- 

 out 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 variegated marls are succeeded l^y a 

 sandstone ledge at least 100 feet in height, yielding black logs of very 

 fine structure. At this point these sandstone beds constitute an escarp- 

 ment 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 mainlj^ of loose 

 material somewhat resembling dried mortar, for which reason I have 

 designated them mortar beds. They are, however, ver}- irregular in struc- 

 ture 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 I regard as true Shinarump, and petrified wood 

 was found above the limestone ledge. 



A wider acquaintance with this part of the member 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, not only the 

 variegated marls, but also the shales of the conglomerate member, which 

 become transformed into marls, are more or less calcareous; and as 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 Ave were to look for its homo- 

 logue in the Trias of the Old World we should find it in the Muschelkalk, 

 while the conglomerate member might well be compared with the Bunter- 

 sandstein, and the Painted Desert formation with the Keuper, to which 

 the French term Marnes Irisees is only locally applicable. 



In the extensive exposures on Leroux Wash these relations are 

 brought out with great force. Overlying the true variegated marls which 

 stretch out for a distance of 3 miles across the broad eroded valley, the 

 limestone series comes in graduallj^ and scarcely differs, except in the 

 degree of calcareousness, from the underlying beds; but the limestone 

 ledge is ultimately reached and is sharp and definite. It has a thickness 

 of about 10 feet. Over it lie very heavy beds of calcareous materials, 



