MiNUELEFF] ' SITES OF CAVATE LODGES. 219 



it there is another belt of jmrple-gray saiidstoue about 12 feet thick. 

 The top of this saudstoue forms the gTouiul surface south of the point 

 shown iu the diagram, while on the north and east it forms the tioor of 

 the upper tier of cavate lodges. 



On the southern side of tlie canyon the lower purple stratum shows 

 three distinct substrata; the ui)per is reddish purple and about 3^ feet 

 thick, the middle is purple gray, about 7 feet thick, and apparently 

 softer than the upper and lower strata. The lodges occur in the 

 middle purple substratum, their floors composed of the upper surface 

 of the lower stratum and their roofs of the under surface of the upper 

 stratum. Those on the north side arc similarly placed, their roofs being 

 about 3 feet below the white, except that iu several iustanc^es the upper 

 part of the purple up to the v/hite has fallon, making the cavity larger. 

 This has occurred, however, since the abandoumeut of the caves, and 

 the debris, still fresh looking, is in situ. 



The formation in which the lodges occur is not of volcanic origin, 

 although the beds composing it were perhaps deposited by hot springs 

 during the period of great volcanic activity which produced San Fran- 

 cisco mountain in central Arizona and the great lava flows south of 

 it. In view of the uncertainty on this point and the further fact that 

 almost all the cavate lodges heretofore found were excavated iu tufa, 

 ash, or other soft volcauic de])osits, the report of Mr. Joseph S. Diller, 

 petrographer of the U. S. Geological Survey, will be of interest. It is 

 as follows: 



The coarse-grainetl specimen is sandstone, tliat of medium grain is argillaceous 

 sandstone, and the Jine-grained one is calcareous clay. The coarse-grained friable 

 sandstone, in which the lodges have been excavated, consists chiefly of subaugular 

 and rounded grains of quartz and feldspar with a small proxiortiou of black particles. 

 Many of the latter are magnetite, while the others are hornblende and various ferro- 

 magnesiau silicates. I did not detect any fragments of volcanic origin. 



The specimen of argillaceous sandstone is made up of thin layers of fine-grained 

 sand of the same sort as the first, alternating with others containing considerable 

 clay. In the clay layers, a trace of carbonate of lime was found here and there, 

 forming a transition of the calcareous clay. 



The calcareous clay when placed in acid effervesces vigorously, but when allowed 

 to stand the eftervescence ceases iu a few minutes and the insoluble white clay 

 remains. 



All the strata composing this formation are very soft; the purple- 

 gray material of the middle layer is so soft that its surface can 

 be rubbed off with the hand. They are also minutely stratified or 

 laminated, and the laminai are not well cemented together, so that a 

 blow on the roof of a cavity with a stotie or other implement will bring 

 ott' slabs varying from half an inch to an inch and a half in thickness. 

 These thin strata or lamiiue are of unequal hardness, weathering in 

 places several inches into the face of the rock in thin streaks of a few 

 inches or less. The middle purple stratum exhibits this quality some- 

 what more decidedly than the others, and this fact has doubtless 

 determined the selection of this stratum for the location of the lodges, 



