EFFECTS OF EARTHQUAKES AND VOLCANOES. 91 
oscillations and changes of level are known to have occurred else- 
where on the surface of the globe, and it may be conjectured that 
they have not been uncommon. But of the two movements, upward 
and downward, if we may judge from characters of the strata to 
which we have access, the former have been more frequent than the 
latter. Organic remains of marine origin are found imbedded in 
greatabundancealong the sides or on the summits of mountains, but 
this is not quite decisive. We do not know what submerged 
continents may now be covered by the waters of the ocean. The 
conclusion may however be regarded as warranted by the facts, 
which living geologists have generally regarded themselves as 
under the necessity of adopting — that the mountains which are 
called primitive, though existing probably 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. 7/ is probable that the caitsps which are now 
active in the production of the phenomena of earthquakes and 
volcanoes, have effected import ant changes 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 present form, a class of rocks (the trap rocks ) 
that were the subject of fierce contention between the rival 
schools of Hut ton and Werner. 
We have now come to one of the most difficult problems in the 
science ofgeology ; that of accounting for the changes that havejust 
been stated and described. The unstratified rocks, and especially 
granite, have been heaved out of the bowels of the earth, carrying 
with them , and before them, strata that had been accumulated at the 
bottom of the ocean, and have thus formed the existing continents. 
How? What is the nature of the force by which effects so vast 
and magnificent have been produced ? There will be given by 
way 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 Hocks. 
At a distance of about fi ft 3?" miles from Freyburg where Wer- 
ner taught mineralogy, the Erzgeberg mountains, rich in the me- 
tal ores, separate Saxony from Bohemia ; the chain being about 
one hundred 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 ba«alt upon their summits. The basalt is in the form of 
huge blocks, two or three hundred feet in thickness. It occurs 
on fourteen different mountains, scattered over an area of 600 
square miles, but the surface of all the basalt taken together does 
not much exceed a single square mile. The mountains themselves, 
are' primitive, being constituted of granite, gneiss, and mica and 
clay slate. The basalt sometimes reposes directly on these rocks^ 
