142 



WALLACE W. ATWOOD 



some fissure associated with the center of activities. This relation- 

 ship indicates that Red Mountain was developed during the later, 

 rather than during the earlier, phases of vulcanism in the region. 

 The general position of the layers of tuff has been referred to, and 

 the directions of the strike and dip have been plotted at several points 

 on the topographic sketch (Fig i). The layers near the base, and as 



Fig. 3. — Northeast side of Red Mountain, showing structure. 



near the center of the mountain as it is possible to get, decline 4°. 

 They are, probably, some of the ealiest deposits made about this 

 vent. As the fragmental material accumulated, it formed steeper 

 and steeper slopes about the rim of the crater, and today the expos- 

 ures show an increasing dip from the base to the summit, passing 

 gradually through angles of 5°, 10°, 15°, up to 20°. The major 

 divisions in the tujEf appear, from a distance, to be from 15 to 20 feet 

 thick. On closer examination subdivisions may be recognized 

 down to an average thickness of from one to two inches. Within 

 a layer or bed of tuff there is no noticeable assortment of material. 



