314 D. W. JOHNSON VOLCAMC NECKS OF MT. TAYLOR REGION 



Number 4 (figure 5). This butte resembles number 3 in being com- 

 posed of both agglomerate and columnar basalt. A detailed description 

 of the structural features of the different l)uttes would in most cases be 

 essentiall}^ a repetition of that given above for number 3. Accordingl}' 

 only critically important jioints will be specifically mentioned in the 

 remaining descriptions. 



The horizontal Cretaceous beds are well exposed about the 1)ase of 

 number 4, and in some places well wp the sides. This is especially true 

 (Ui the south side, where horizontal sediments are seen well up toward 

 the summit, making a vertical contact with the igneous core of the butte. 



Number 5 (plate 30 and figures 6 and 7). This butte is of special 

 interest because of the vmusually good exposures it alfords. On the north- 



FiGUitE 6. — DiagraiiiiiKitic Sketch to shoir Rclutinii of siin-oiiniling ]iori.:ontaJ Sedhiieiifs 

 to igneous Core of Butte niiinlicr J and the comijle-c Structure of the Core. 



eni and western sides the yellow sandstones and shales are beautifully 

 exposed and show practically no disturbing effect of the intrusion. Gul- 

 lies have cut back tlirough the sediments to the butte, ending abruptly 

 against the more or less vertical wall of igneous rock. These give peculiar 

 niches or alleyways, flanked on either side by steep walls of horizontal 

 sediments, with a back wall of igneous rock formed b,y the side of the 

 butte. The precise contacts are sometimes well shown, and are seen to 

 be essentially vertical. The sediments are usually cut off square, without 

 any evidence of disturbance whatever, but occasionally they show a slight 

 dip away from the contact. In one place a distinct stringer or dike is 

 seen running from the butte out into the sediments. 



The upper part of the butte shows fair vertical columnar structure in 

 places, and vertical columns are found well down the butte on one side 



