146 Reports on the Geology of the State of J^aine. 



intermingling with the others, in such a manner as to leave no 

 doubt of its comparative newness.* Many striking facts of this 

 kind are presented, and the subject is well illustated by diagrams. 

 Masses of granite and slate are often included in the dykes, form- 

 ing an interfused kind of breccia, while the slate is not unfre- 

 quently converted into jasper, hornstone and chert, besides being 

 abundantly charged with pyrites ; the trap itself assuming a 

 spongy or vesicular appearance, showing evident marks of fu- 

 sion. After mentioning several localities in reference to this 

 point, Dr. Jackson says, " it will be observed, that the slate rocks 

 where they are in immediate contact with the trap dykes, are 

 hardened into a kind of green -flinty slate, while more remote 

 from them, the slate is less hard, and is converted into novaculite 

 or hone stone, valuable for fine hones or oil stones, and presenting 

 various stripes of blue, brown and green colors which run in the 

 direction of the strata." Those who are accustomed to geolo- 

 gical observations will readily understand with what satisfaction 

 the following facts were recorded. 



"Our excursion to Bald Head was exceedingly instructive, since we 

 there discovered the relative ages of most of the trap-dykes, the direc- 

 tions of which we had before been accurately recording, knowing that if 

 we put down exactly what we found in nature, some useful instruction 

 would certainly result. Here, then, to our surprise and gratification, 

 we met with absolute proof of their different ages, a result which I 

 had only hoped to have obtained after a long research. This locality 

 solved at once, by absolute demonstration, this important problem ; for 

 here we saw the various.dykes cutting across each other, in such a man- 

 ner, as to prove their several different eruptions; and we may confidently 

 affirm, that four or five distinct eruptions of molten trap rocks have burst 

 through the strata of Maine." 



The chemical changes effected upon the limestone at some of the 

 quarries where the dykes are now left standing like immense walls, 

 are thus mentioned. "The limestone at its junction with the 

 trap is closely cemented to it, and is converted into a perfectly 

 white crystalline variety, which loses this character in proportion 

 to Its distance from the dyke. The effect was the same in the 



* One of these dykes is 500 feet wide, and extends completely tlirough a moun- 

 tain of grayvvacl<e and clay slate 1900 feet high, rising higher above the sea than be 

 }aad ever seen that rock (trap) attain. 



