30 BUREAU OF AMERICAN ETHNOLOGY [bull. 54 



In the northern and western part of New Mexico are many old 

 volcanic vents, and it is likely that the tuffs of the Pajarito plateau 

 came not from a single vent, but from a number of vents about the 

 rim of the basin, a suggestion long ago made, the confirmation of 

 which time did not permit in the present work. 



In the vicinity of El Rito de los Frijoles the upper half of the 

 tufa-sheet is heavier, harder, and 'mostly of darker color than the 

 lower half. Furthermore, some zones in the upper half are harder 

 than others, while the lower half is more uniform in this respect. This 

 difference in hardness is very important in connection with the cliffs 

 and terraces hereinafter discussed. Throughout the formation the 

 portions fully exposed to the weather are covered with a thin, ill- 

 defijied, somewhat hardened layer one-eighth to one-half inch in thick- 

 ness, which protects it from more rapid weathering. The hard zones 

 in the upper half are partly, if not wholly, due to a similar process of 

 "case-hardening." In some vertical cleavage planes tliis hardening 

 was found to have occurred on both sides of the minute crevices. In 

 view of these facts the whole aspect of the cliff points to the likelihood 

 that the hardening has been caused by water following in the one 

 case vertical cleavage planes, in the other horizontal planes which may 

 possibly represent the lines separating the ashes or mud of successive 

 showers or flows. 



As the ui)per part of the Santa Fe marls is considered early Pliocene, 

 these overlying tuffs must be of later Pliocene or post-Pliocene age. 



In many places intrusive basalts have been injected into or through 

 the Santa Fe formation and the tufa. An excellent place to study 

 the relation of the sedimentaries, the tufa, and the basalt, is in the 

 vicinity of Buckman, at the crossing of the Kio Grande on the present 

 road from Santa Fe to El Rito de los Frijoles. The intrusive character 

 of the basalt is well shown, however, in Frijoles canyon, just above 

 its mouth. There vertical contacts of masses of basalt with both 

 sandstones and tufa are found well exposed, and horizontal sheets of 

 basalt extend off into the tufa and between strata of sandstone. The 

 basalt is hard and heavy, varying on weathered surfaces from light 

 gray to black and covered in many places with superficial cavities up 

 to half an inch in diameter, from the leaching out of some of the 

 mineral constituents. It represents probably more than one flow. 

 Nearly aU of the basalt is in the olivine group. The first exposure 

 in descending the canyon of El Rito de los Frijoles, however, is a 

 sheet of very dense, fine-grained basalt which should probably be 

 classed as a glassy basalt, showing in a gully on the northern side, half 

 a mile or more above the upper falls. This dense material appears to be 

 that which has been used in the manufacture of the "clinking stones" 

 found in the old ruins of the canyon, and which were probably used 



