555 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Sf.r. 



the southwest and base toward the northeast. The "Mon- 

 arch" is a large fir whose exposed, preserved length is ninety 

 feet and whose diameter at the base is about ten feet. It 

 also has the orientation of the trees described above. In all 

 of these trees the gradual replacement of the woody material by 

 silica carried by waters which percolated through the covering 

 of tuff-breccia has been so complete that the fibers and peculiar 

 texture of the various species have been retained. The di- 

 rection of all of the trees in the "forest" was measured and 

 in all cases was found to lie between N. 30° E. and N. 45° 

 E., with tops toward the southwest. It is evident from these 

 facts that the volcanic mud and pumice came in a great 

 volume from the northeast. A study of the vicinity shows 

 that a lava lies beneath the tuff-breccia and light gray pumice. 

 A section in a small creek, a hundred yards south of the petri- 

 fied trees proves that the forest grew upon a soil formed 

 from this lava. The lava was probably a basalt, but the rock 

 is so badly weathered that it is impossible to classify it with 

 certainty. How long it takes to form from such a lava a 

 soil sufficient to maintain a great forest is an unknown 

 factor, but it must be estimated at least in terms of hundreds 

 of years. The "Queen of the Forest" was probably at least 

 a thousand years old when the great catastrophe occurred 

 which wiped out this Pliocene forest. From such data, we 

 may assume that the time interval between the lava flow and 

 the deposition of tuff and tuff-breccia must be estimated in 

 terms of a few thousand years as a minimum. The time 

 interval represented by the Neohipparion gidleyi beds of 

 Sonoma Mountain is probably of about the same order as the 

 above described case. We must be generous in the use of 

 time when we are concerned with geologic estimates and such 

 an interval as indicated above is probably not sufficiently long 

 to justify minute sub-division of the geologic scale. In broad 

 correlations it is not possible to consider many of these cases. 



CORRELATION 



As was shown above, the marine Merced is distinctly inter- 

 fingered with the basalts and tuffs of the Sonoma group. 

 Around Freestone, tuffs containing Merced fossils were found 

 interbedded with sandstones and sandy shales of Merced 

 age. At Spring Hill, west of Petaluma, Merced strata rest 



