34 BUREAU OF AMERICAN ETHNOLOGY [bull 54 



material after breaking through the harder crust, so that the interior* 

 diameters of most of the cavities are greater than the tliameters of 

 the entrances. The great ceremonial cave at the upper end of the 

 valley has been excavated chiefly by the wind in the softer material 

 between two of the hard zones before referred to. 



Whatever may be said of the past, all these forces of erosion 

 are evidently working quite slowly at the present time. The ]:)laster- 

 iiig about the entrances to some of the caves remains mtact, though 

 the walls of the buildings which once stood before them have crumbled 

 badly. Whether or not erosion is as rapid as formerly, at any rate 

 the canyon has been cut by means of processes still at work in the 

 region, and if there is a difference m the rate of erosion, no reason 

 exists for considering the dift'erence very great. 



The same forces of erosion have an indirect influence on the vege- 

 tation, (1) by the production of dry mesas, better-watered canyons, 

 and slopes varying in steepness and direction; and (2) by the pro- 

 duction of exposures varying from indurated rock to fine soil. The 

 chief exposure of indurated rock is the tufa, and, to a less extent, 

 basalt, with still less of the sedimentary formation. The quartz 

 crystals contamed m the tufa form a large constituent of the soil, 

 which is consequently very sandy. The dismtegrated tufa forms the 

 dominant soil of the region. On stream terraces, flood plains, and 

 mesa tops the soil is rather fine. On canyon sides and talus slopes 

 there is a larger admixture of angular fragments and of pebbles of 

 tufa of widely varying size. The accumulations of humus soil are 

 small; these occur here and there along the stream but are so insig- 

 nificant as to deserve but little consideration. It is quite probable 

 that occasional floods, which affect the banks of the streams where 

 humus would otherwise accumulate, have prevented the formation 

 of such soil, and away from the banks of the streams the aridity of 

 the region would act as a preventive. At higher altitudes, where 

 the humidity is greater and vegetation more abundant, there are 

 larger accumulations of humus along the streams and on the forest 

 floor. It is m stich situations that fungus forms are much more 

 abundant. 



In the rums are found selenite flakes, turquoise, pottery, and 

 implements made of tufa, basalt, obsidian, schist, quartz, quartzite, 

 and other rocks. The tufa, basalt, and obsidian were obtainable in 

 the vicinity. Large beds of obsidian are reported elsewhere in New 

 Mexico. The source of the selenite and clay is not definitely known, 

 but probably they were not obtained m the immediate vicinity. 

 Turquoise is found at several places in New Mexico. Beds of bowlders, 

 including schists, quartzites, and other materials, such as have been 

 used in making various implements, are found along the Rio Grande 

 not far distant, as at Buckman. Some of the pottery contains much 

 mica in tiny flakes. 



