EFFECTS OF EARTHQUAKES AND VOLCANOES. 
91 
oscillations ami changes of level are known to have occurred else¬ 
where on the surface of the glolie, and it may be conjectured that 
tliey have not been uncommon. Hut of ibe I wo movements, upward 
and downward, if we may judge from cbaracters of the strata to 
whicli we have access, tlie former liave Ijeen more frequent than the 
latter. Organic remains of marine origin are found imbedded in 
greatabundancealong tbe sides or on tlie summits of mountains, but 
this is not (juite decisive. ^Ve do not know wliat submerged 
continents may now be covered by tlie waters of the ocean. The 
conclusion may however he regaialed as warranted hy the facts, 
whicli livinc: geologists have generally regarded themselves as 
under the necessity of adopting—that the mountains which are 
called primitive, though existing piobably in the form of rocks 
within the bowels of the earth., have been forced up through the 
transition and secondary strata, producing that confusion and dis¬ 
order which are so strikingly exhibited in the neighborhood of 
the great mountain chains. 
50. Prop. V. It is probable that the causes luhich are now 
active in the prodnetion of the phetioinena of earthquakes and 
volcanoes, have effected important chane^es in the features of the 
globe, in particular that they raised the primitive mountains 
out of the bed of the sea. They also brought into existence 
under their prese?^ form, a class of rocks (the trap rocks) 
that were the subject of fierce contention between the rival 
schools of Hutton and ll'erner. 
We have now come to one of the most difilcult problems in the 
science ofgeology; that of accounting for the changes that have just 
been stated and described. Tbe unstratified rocks, and especially 
granite, have been heaved out of the bowels of the earth, carrying 
with them . and before tbem, strata that had been accumulated at the 
bottom of the ocean, and have thus formed tbe existing continents. 
IIow ? Wbat is the nature of the force by which ellects so vast 
and magnificent have been produced? There will be given by 
wa}" of introduction to the discussion of this question, a brief ac¬ 
count of the controversy that was maintained with the utmost 
degree of vehemence and bitterness, about half a century ago, re¬ 
specting the origin of the Trap Pocks. 
At a distance of about fifty miles from Freyburg where Wer¬ 
ner taught mineralogy, the Krzgeherg mountains, rich in the me¬ 
tal ores, separate Saxony from llohemia ; the chain being about 
one bundred and twenty miles in length. Some of the highest 
peaks of the chain, or of the spurs that make out from it, have a 
cap of basalt uiion their summits. The basalt is in the form of 
huge blocks, two or three hundred feet in thickness. It occurs 
on fourteen ditl'ercnt mountains, scattered over an area of GOO 
square miles, but the surface of all the basalt taken together does 
not much exceed a single square mile. The mountains themselves, 
are prim.itive, being constituted of granite, gneiss, and mica and 
clay slate. The basalt sometimes reposes directly on these rocks_ 
