276 



UNSTRATIFIED ROCKS 



canic blocks. Associated with this plug of lava may be preserved 

 the lowest lava flows or tuffs of which the cone was originally 

 built up. If the land upon which the volcanic neck stands be 

 covered by the sea or other body of water, the remnant of the 



Fig. 121. — Jointed lava flow. Passaic River, New Jersey. (U. S. G. S.) 



cone will be buried beneath sediments, and a volcanic island 

 may be similarly cut down and covered with sediments. Subse- 

 quent upheaval and denudation may at a long subsequent time 

 once more expose the buried cone to view. Several examples of 

 this have been found in Great Britain. 



