THE ULDEK ME60ZOK' OF ARIZONA. 33 



This l)rilliantly colored petrified wood comes chiefly from the true 

 coiijilomei-ates; and, as already remarked, that of the so-called Middle 

 Forest, wiiich lies farther to the east and lias weatliei'ed out of the varie- 

 gated marls, is less brilliant, though scarcely less abundant. At the base 

 of these same mai'ls on Leroux Wash, especially at tlic lower end of the 

 system, great (luaiil iti(>s of logs lie out upon the plain. Tliey have a 

 ivddish-brown color, ai'e very large, and look at a distance like so many 

 rusly locomotive boilers. They are broken aci'oss into sections. Most of 

 the wood at this hoi'izon, however, is not colored, and it has u.sually 

 undergone a higher degree of disintegration than the harder trunks from 

 the conglomerates. It shows the structui'e admirably, at least to all out- 

 ward appearances, and the sections are usually split up into a large num- 

 ber of blocks and ultimately reduced to a mass of c-hips and splinters, 

 which look so natiu'al that they would not be suspected of l)eing petrified 

 unless picked up and examined closely. Many of the smaller l)uttes seem 

 to have l)een occasioned by the presence of logs, which weighted the 

 underlying marls and tended to prevent their being washed or blown 

 away. The result is that many of these buttes have such logs lying on 

 their summits, with the disintegrated material rolling down its slopes. 



In my report on the Petrified Forests of Arizona (p. 15) I mentioned 

 the statements made by Mollhausen and Marcou that they had seen 

 trunks standing erect and evidently in place, and I quoted (p. 16) Doc- 

 tor Newberry's conclusion, agreeing with mine, that this phenomenon 

 probably did not occur. So far as the conglomerates are concerned, 

 I have seen no reason for altering this conclusion, although I would not 

 be as positive now as I was then that cases of the kind will not be found. 

 But with regard to the trunks entombed in the variegated marls, or 

 next horizon above the conglomerates, we practically demonstrated 

 that erect stumps do occur in them. Within a quarter of a mile of 

 the butte from which Mr. Brown foimd the best preserved vertebrate 

 bones there is a small area, probably 30 or 40 acres, which contains 

 a group of twenty or more such stumps. They are low, rarely rising 

 more than 4 feet above the grovmd, but some of them are large, having 

 a diameter of from 3 to 4 feet. Nearly the entire trunk al)Ove these 

 stumps, as well as all the branches, has wholly disappeared, IjuI the 

 ground is strewn with small chips and bloc'ks. It is a somewhat level 



HON xi.viji — 0.5 3 



