Igneous Hjections, Volcanoes. 105 
ejections the old one of viscous rock underneath the earth’s 
crust; but viscous rock at first as a layer, and later as rem- 
) 
appears to be true of most of them), and a consequence of the 
later movements of lateral pressu 
nucleus surrounded by a superficial fluid envelope, according as the solidification 
th t the surface or center; but in either case, as I have already intimated, 
e “yaaa when first formed must necessarily have reposed on a fg 
pai a phage : : 
e assi a 
graph on p. 33 speaking of the isolated sources of yolcanoes], to be its pres- 
ent condition, that of a solid mass containing numerous cavities filled with fluid 
cenniescennt matter, and either entirely insulated or perhaps communicating In 
Me cases by obstructed channels.” These cavities are made the sources of the 
* Volcanos, 2d ed., 8vo. 
; 264, 268. 
t ills and dikes 0 te p” (as they are ordinarily called) have great length 
and in many } the Connecticut valley they i sind angage: 
any lines lai i Connecticut, by Perciv 
ical ,—as laid down, especially for 4 t febaage tog 
regic port. p 
m is reproduced in the writer's Manual of Geology, page 20. At the east 
pe ny bend in the dikes, south of the middle of the map, are the Hanging Hills 
eriden, 900 to 1,000 feet high, situated about 20 miles north of New Haven 
