38 
The American Geoloirist. 
July, 1898 
-;:o->. 
Fig. 2. The Isleta volcano. In the middle ground the abrupt escarpmout of the 
lava-topped mud fl'>ws from the volcano. 
Fig. 3. Portion of the same as shown in fiarure 2 to show the fragments of basalf 
scattered in the stratified mud. 
water in which trees might become impregnated with siUca, 
or more probably a mass of such pasty material charged with 
silicious water would be a still better means of altering im- 
bedded trunks. Of course, the age of these flows is still to 
be determined, though it may safely be placed at an earlier 
period than that in which the river gravels were deposited, 
that is, earlier than the post-glacial or Champlain period. It 
would appear that the silicification of the forest beds must 
have been in a general way contemporaneous with the sand 
accumulations, but the trunks are sometimes found in sand- 
stones supposed to be not later than the Cretaceous. Still 
further, the finding of ears of corn imbedded in the lower sur- 
face of the flow of lava in certain places might then be thought 
to take human occupation back to that period, but it is plain 
that at present no such wide generalization is warrantable, 
though the above-mentioned facts point the way to the final 
