126 Mr. Dana on the Analogies between the 
however expect greater regularity than exists in acknowledged 
volcanic regions, and granites may be found inserted among all 
the schists, as dykes or mountains of trap and basalt are intruded 
among stratified deposits. 
This subject is finely illustrated in Northern California. After 
passing twice from talcose rocks over syenite to granite, and in 
one instance back again to uncrystalline talcose or hornblende 
rocks, we made the same transition a third time. ‘The features 
of the country were quite mountainous, and the mountains abrupt 
throughout the region of talcose and syenitic rocks; but the 
eranite at the centres stood out in bold contrast with these serra- 
ted ridges, its lofty needle summits, white almost like snow from 
its albitic rock, peering above the green foliage of the forest about 
us, forming one of the grandest scenes I ever witnessed. 'The 
features of the region were too much like Tahiti not to be at 
once reminded of that island. From the granite, the route led 
over syenites and hypersthene rocks to talcose slate and a com- 
pact greenish rock resembling nephrite; from them to a stratified 
jasper of red and yellow colors covering large areas. ‘The jasper 
rock is composed of layers two or three inches thick, which con- 
stantly coalesce and subdivide ; it was obviously an aqueous de- 
posit. Itis associated very closely with talcose slate containing 
beds of serpentine, and not far off occurs the protogine to which 
T have alluded, and shown to be of derivative origin. 
May we not safely set this down asa vast region of igneous 
action; the talcose rocks and slates and the jasper forming its 
outer border, and the granite the centre—analogous in some de- 
gree to the stratified circumference and compact basaltic centre 
of Tahiti? Does not the absence of crystallization in the outer 
rocks correspond precisely with this theory? Is not this jasper 
the final deposition of the silica into beds of ferruginous clay, 
where the waters had spread and cooled far from the centre of 
heat? and the talcose slates and serpentine associated with the 
jasper, do they not, by evincing the action of heated waters, bear 
us out in this supposition ? 
I would not be understood as implying that here was once a 
voleanic cone and a crater, for it is too well known that eruptions 
take place on a grand scale without forming cones; and indeed 
throughout the Pacific all the larger volcanic mountains are more 
like domes than cones, rising gradually at an angle of ten to four- 
