BASALTIC AND VOLCANIC ROCKS. 271 



SIX are found in the same formation in Europe. This 

 deposite is also called marl, and is extensively used 

 in Virginia and other states for its fertilizing prop- 

 erties. 



CHAPTER XXV. 

 GEOLOGY OF THE UNITED STATES. 



BASALTIC AND VOLCANIC ROCKS. 



Basaltic and Volcanic Rocks. — Evidences of Volcanic Action m 

 the Rocky Mountains. — Trap Rocks. — Bakewell's Definition 

 of Basalt — Of Greenstone. — Localities of Greenstone Trap — 

 In Massachusetts — New-Jersey — Columbia River — Nova 

 Scotia. 



The principal deficiencies in the geological for- 

 mations of the United States," says Professor Sil- 

 liman, are in the absence of active volcanoes, as 

 well as most of the members of the upper second- 

 ary. However delightful active volcanoes, with 

 their earthquakes and eruptions, may be to specu- 

 lative geologists, the sober, unscientific population 

 may well rest quite contented without them, satis- 

 fied to barter the sublime and terrific for quiet and 

 safety. Although the soils formed from decompo- 

 sed lava are often fertile, and the vine flourishes, 

 and the clusters smile most remarkably on the 

 flanks and at the feet of the volcanic mountains of 

 warm coimtries, these influences are too local to 

 be of much importance to agriculture. 



" Within the United States proper, including the 

 states and territories beyond the Mississippi and 

 east of the Alleghany Mountains, there is not, so 

 far as we know, a single active volcano, nor even 

 an unequivocal crater of one that is dormant. Both 

 north and south of our limits there are, on the Pa- 



