PLUTONIC ROCKS. 
31 
The absence of cones and craters, and long narrow streams 
of superficial lava, in England and many other countries, is 
principally to be attributed to the eruptions having been 
submarine, just as a considerable proportion of volcanoes in 
our own times burst out beneath the sea. But this question 
must be enlarged upon more fully in the chapters on Igne¬ 
ous Rocks, in which it will also be shown, that as different 
sedimentary formations, containing each their characteristic 
fossils, have been deposited at successive periods, so also vol¬ 
canic sand and scoriae have been thrown out, and lavas have 
flowed over the land or bed *of the sea, at many different 
epochs, or have been injected into fissures; so that the igne¬ 
ous as well as the aqueous rocks may be classed as a chrono¬ 
logical series of monuments, throwing light on a succession 
of events in the history of the earth. 
Plutonic Rocks {Granite^ etc).—We have now pointed out 
the existence of two distinct orders of mineral masses, the 
aqueous and the volcanic: but if we examine a large por¬ 
tion of a continent, especially if it contain within it a lofty 
mountain range, we rarely fail to discover two other classes 
of rocks, very distinct from either of those above alluded to, 
and which we can neither assimilate to deposits such as are 
now accumulated in lakes or seas, nor to those generated by 
ordinary volcanic action. The members of both these divis- 
^ ions of rocks agree in being highly crystalline and desti¬ 
tute of organic remains. The rocks of one division have 
been called plutonic, comprehending all the granites and 
certain porphyries, which are nearly allied in some of their 
characters to volcanic formations. The members of the 
other class are stratified and often slaty, and have been 
called by some the crystalline schists^ in which group are in¬ 
cluded gneiss, micaceous-schist (or mica-slate), hornblende- 
schist, statuary marble, the finer kinds of roofing slate, and 
other rocks afterwards to be described. 
As it is admitted that nothing strictly analogous to these 
crystalline productions can now be seen in the progress of 
formation on the earth’s surface, it will naturally be asked, 
on what data we can find a place for them in a system of 
classification founded on the origin of rocks. I can not, in 
reply to this question, pretend to give the student, in a few 
words, an intelligible account of the long chain of facts and 
reasonings from which geologists have been led to infer the 
nature of the rocks in question. The result, however, may 
be briefly stated. All the various kinds of granites which 
constitute the plutonic family are supposed to be of ig¬ 
neous or aqueo-igneous origin, and to have been formed un- 
