182 



NATUBALT SCIENCE NEWS. 



The Petrified Trees of Arizona. 



At a recent meeting of the New 

 York Academy of Sciences a paper on 

 Some Features of the Arizona Plat- 

 eau was read by L. S. Griswold. 



In general the plateau surface is 

 between 6,000 and 7,000 feet in ele 

 vation above sea level and strikes one 

 as being remarkably smooth for so 

 high elevation; there are large 

 stretches of nearly level or gently 

 rolling country, diversified, however, 

 by mesas and outliers, with escarp- 

 ments rising between 50 and 200 

 feet, shallow but broad old stream 

 channels now little used and leading 

 to canons with percipitous walls. 

 On the plateau top are numerous vol- 

 canic elevations, varying iu age from 

 the young cinder cone to the denud- 

 ed stock. Over the d'strict silicified 

 wood is well known, occurring at the 

 base of a gravel and sand horizon, 

 little consolidated, belonging to the 

 late Tertiary or Pleistocene times, 

 and lying with slight unconformity 

 in part upon probable Triassic strata 

 and in part upon Carboniferous, the 

 older formations being little dis- 

 turbed. 



The trees now petrified originally 

 grew to large size, eight or nine feet 

 in diameter for the largest probably 

 conifers, and perhaps not very differ- 

 ent from the forest growth of part of 

 the present plateau. This ancient 

 forest was apparently thrown down 

 by the wind, for tree butts are com- 

 mon in horizontal position while only 

 one was found erect. The gravel 

 and sand covering would seem to 

 have come soon, for only a few have 

 fillings of sediment in hollows or give 

 other indications of decay; the logs 

 were buried at least fifty or sixty feet 

 deep. The weight of the overlying 

 sediments crushed the trees so that 

 the horizontal diameters are common- 

 ly greater than the vertical as they 

 are seen in place. Silicification was 

 probably accomplished by percolat- 

 ing surface waters, as the logs are 

 distant from volcanic vents, as far as 

 known to the writer; then no hot 

 water deposits were seen accompany- 

 ing the logs, and the distribution as 

 seen over many miles and reported 

 much more widely would also mili- 

 tate against the theory of change by 

 hot water. — Scientific American. 



We are indebted to the Drake Company of 

 Sioux Falls, S. D. for the use of the plates from 

 which the above views were printed. For a 

 more extended account of the Petrified Forest 

 see Natural Science News of Dec. 7th. 



The Ruined Gila Cities. 



The attention of people interested 

 in archaeology and ethnology gen- 

 erally has long been directed to 

 the ruins of the cliff dwellings in 

 northern Arizona and southern Colo- 



I i , MM 



Natural Bridge of Petrified Tree lO 



yievysoof the Petrified 



