Introductory Remarks. 



403 



the general opinion was, that they originated from the crystalization 

 of their ingredients dissolved in water. At this day the belief in 

 their igneous origin has become nearly as universal. In regard to 

 the trap rocks, indeed, this opinion is almost unanimous. Why there 

 should be any more hesitation in assigning a similar origin to gran- 

 ite, I confess myself unable to imagine. I should almost as soon 

 deny that the red rays of the spectrum proceed from the sun, after 

 admitting that the six other colors were produced by that luminary. 

 I am constrained thus early to express my conviction of the igneous 

 origin of all the unstratified rocks : for I have found that opinion mar- 

 velously to simplify the history of these rocks ; and to clear up may dif- 

 ficulties inexplicable on any other theory. To regard these rocks as 

 they occur in the primary secondary and tertiary classes, as independ- 

 ent of one another, and of the same age of the formations in which they 

 occur, and thus to describe them as primary, transition, secondary, 

 &c. produces in this part of geology a perfect chaos. But to regard 

 them all as merely varieties of the same melted mixture, whose pe- 

 culiarities resulted from the modes in which they were cooled, and 

 crystalized, and intruded among the stratified rocks, does certainly 

 relieve the mind of a host of doubts and difficulties, and render the 

 history of these varieties comparatively easy, whether the theory be 

 true or false. On this supposition we are no longer surprised to find 

 it impossible to draw any definite line between the different varie- 

 ties, nor to find them all united in the same mountain mass. 



It must not, however, be understood that this view of the subject 

 implies that all the unstratified rocks are of the same age. For in 

 this respect there is evidence of nearly as great diversuy as exists 

 among the stratified rocks. And their intrusion among the stratified 

 rocks affords an important clue for determining their relative ages. 

 It is obvious, however, that the intrusion of the former among the 

 strata of the latter, only proves that the unstratified rock was formed 

 posterior to the stratified one. And on this principle it has been 

 shown, that granite has been protruded even since the deposition of 

 the chalk : while basalt has cut through even the supercretaceous 

 rocks ; and finally, the products of existing volcanoes overspread 

 diluvium and alluvium. 



So well satisfied am I of the correctness of these views respecting 

 the unstratified rocks, that I have been strongly tempted, according to 

 the suggestion of Dr. Macculloch, to treat of all those that occur in 

 Massachusetts as a single family ; being convinced with him, that 



