102 



Waring — Lavas of Morro Ihll and Vicinity. 



the rock grades into homogeneous pink tuff, of the same char- 

 acter as the fragments it encloses. The greater part of the 

 slopes southeast of this lower hill near Morro Hill is composed 

 of the pink tuff, which is mainly of a uniform color and 

 texture, but along its borders is agglomeratic in character, as is 

 shown in fig. 5. A slide of material from locality 5 shows it to 

 be andesite with felsitic and glassy groundmass and a consider- 



FiG. 5. 



Fig. 5. Tuff agglomerate near tlie uorth margin of the andesite flow, 

 southeast of Morro Hill. 



able proportion of fine crystals of light-green epidote. Some 

 magnetite is also present. 



The distinct difference in petrographic character of the lava 

 composing Morro Hill and that of the lower hill to the south- 

 east indicates that they represent two phases of intrusion. As 

 there are no other evidences of volcanic activity in the imme- 

 diate vicinity, it seems possible that each hill has been built up 

 over a small vent, for the fragments of dioritic mineral in the 

 rock at locality -i indicate that the lava here has been forced up 

 through the diorite, and the shape of the larger hill is believed 

 to indicate that its lava also issued from a vent beneath the 

 present capping. The restricted areas covered by the lavas 

 indicate that the locality was the seat of only minor activity. 

 So far as is known to the writers this is the only occurrence of 

 lavas of the kind for a radius of at least 20 miles. At this dis- 



