80 GEOLOGY. 
a number of trunks of which the fragments were all in opposition, and the tree complete from 
root to summit. Of these, some had a diameter of at least three, and a length of more than 
forty feet. 
I examined these specimens with some care to determine, if possible, whether they had 
grown on the spot, as those of Lithodendron creek are supposed to have done by the members of 
Captain Whipple’s party, or whether they had been transported to their positions. In all that 
came under my observation, I failed to find any evidence that they had grown in the vicinity. 
All the trunks are stripped of their branches and exhibit precisely the appearance of those 
transported to some distance by the agency of water. In confirmation of this view I should 
also say I found in the marls, with the entire trunks, rounded and water-worn fragments of 
wood, in some instances silicified and in others converted into lignite. 
I gathered the same impression from all the collections of silicified wood which I observed in 
this formation in Western New Mexico, viz: that all had been transported, but not far removed 
from their place of growth. 
Trap buttes.—A few miles north of the point where we ascended the mesa, we approached a 
series of detached buttes which rose from its surface to the height of several hundred feet, and 
of which the peculiar outlines had attracted our attention, while we were yet many miles west 
of the Little Colorado, These buttes we found to consist of masses of trap at top, beneath 
which was a continuation of the series of variegated marls already given. The trap is, in some 
cases, partially columnar, the columns being vertical, and evidently once formed part of a 
basaltic mesa which covered a large area in this vicinity. The source from which this trap 
was derived seems to have been some point on a line from the crossing of the Little Colorado 
to Fort Defiance, but east and south of our route, as the trap buttes become broader and more 
numerous northeast of our Camps 90 and 91, but were not visible on any part of our route from 
the Moqui villages eastward. 
The amount of erosion which this mesa has suffered since the trap was poured over it is 
measured by the present altitude of the layer of trap (nearly 400 feet) above the general surface. 
Beneath the trap the marls are still horizontal, and but little changed. The composition of the 
basis of the different buttes is everywhere the same, showing conclusively that they are but 
fragments of once continuous strata. 
Although the denudation here indicated is surprisingly great, I think we have incontestable 
proof that the amount of erosion previous to the trap overflow was even greater than what has 
taken place since. On the north the region occupied by the trap buttes is bounded by the 
elevated mesa composed of the Cretaceous rocks which once stretched over all this surface, as 
far as the Little Colorado, and doubtless still further, completely covering the entire series of the 
variegated marls. From the whole of this area the Lower Cretaceous strata, nearly a thousand 
feet in thickness, (and we have even reason to suppose an equal thickness of Upper Cretaceous 
rocks,) were removed by denudation previous to the overflow of the flood of volcanic matter. 
This will appear sufficiently obvious to any one who has an opportunity to examine this 
region, but it was also demonstrated by the discovery in one of these buttes of a patch of 
Cretaceous sandstone overlying the marls, and interposed between them and the trap. The 
sections afforded in the bases of the trap buttes supply the continuation of the series of the 
variegated marls, from the point reached in the section last given to the top of the formation. 
A large butte at Camp 91, of which the castellated summit rises to the height of more than 
ed hundred feet above the plain, exhibits fine exposures of the following strata: 
Feet. 
: re me gertially columbersess si 6x) > aligns ds, c «dentine wind memealwees da dex 160 
2. Green, reddish-brown, and drab, soft ‘alaeiliia sandstones, (indurated marls.)- - 60 
3. — purple, red, and yellow marls, and calcareous sandstones--..-.- ++. +++++ 150 
4, Magnesian edamnatone, pinkish, -oleplnstscdclieiss edi aan chins sube Suis awiieinweds 5 
