KNOWLEDGE OF EARTH STRUCTURE 159 



several lines. The most original contributions were those 

 which dealt with the areal and structural geology of 

 eastern North America, but equally valuable at that 

 time for the broadening of scientific interest were 

 the studies on the volcanic activities of the Hawaiian 

 Islands, published through many years. Perhaps most 

 valuable from the educative standpoint were the exten- 

 sive republications in the Journal of the more important 

 European researches, making them accessible to Ameri- 

 can readers. In volume 13 (1828), for example, a digest 

 of Scrope's work on volcanoes is given, covering forty 

 pages ; and of Daubeny on active and extinct volcanoes, 

 running over seventy-five pages and extending into vol. 

 14. Through these comprehensive studies the nature of 

 volcanic action became generally understood during the 

 first half of the nineteenth century and the original pub- 

 lications in the Journal were valuable in giving a knowl- 

 edge of the activities of the Hawaiian volcanoes. 



Early in the nineteenth century the whole of America 

 still remained to be explored by the geologist. The 

 regions adjacent to the centers of learning were among 

 the first to receive attention and the Triassic basin of 

 Connecticut and Massachusetts yielded information in 

 regard to the nature of igneous intrusion. This basin, 

 of unmetamorphic shales and sandstones, is occupied by 

 the Connecticut River except at its southern end. The 

 Formation contains within it sills, dikes, and outflows of 

 basaltic rocks which because of their superior resistance 

 to erosion constitute prominent hills, in places bounded 

 by cliffs. 



Silliman in 1806 3 described East Rock, New Haven, 

 Connecticut, as a whinstone, trap, or basalt, and 

 accounted for its presence on the supposition that it had 



"actually been melted in the bowels of the earth and ejected 

 among the superior strata by the force of subterraneous fire, 

 but never erupted like lava, cooling under the pressure of the 

 superincumbent strata and therefore compact or nonvesicular, 

 its present form being due to erosion." 



In these conclusions Silliman was correct. With but a 

 limited amount of experience he was able to discriminate 

 between the intrusive and effusive rocks and saw that the 



