120 Igneous Origin of some Trap Rocks. 



ed the outline of similar districts in several countries in Europe, par- 

 ticularly in Germany, Hungary and Italy. 



Analogies with Trap Rocks. 



These analogies are at tliis moment recalled, for the sake of intro- 

 ducing the subject of the present notice. The trap rocks, it is well 

 known, graduate in their mineralogical characters into the acknowl- 

 edged lavas ; and not only into those which are compact and sub- 

 crystalline, but even into the vesicular ; and the columnar lavas also find 

 their counterparts in the rocks of this family. In their geological po- 

 sition too, there is great similarity. Lava currents observe no law 

 but the law of the strongest ; they burst forth, and they intrude, 

 Avherever the expansive power sufficiently impels them ; and they 

 flow over, or accumulate upon any and every species of rock and 

 soil. The trap rocks are characterized by the same irregularity. 

 We cannot say of any particular rocks, that they are the natural asso- 

 ciates of the trap rocks ; for the latter intrude among and repose 

 upon granite and the other primitive rocks ; they are equally recog- 

 nized among the transition rocks ; and they are found with and over- 

 lie the most recent, not excepting bituminous coal, and the tertiary; 

 and even lignite, clay and gravel. They cut granite* and other 

 primitive rocks in two with their dykes ; and the sandstones,f lime- 

 stones, and other rocks, are occasionally severed by the same kind 

 of basaltic wall. 



T7'ap Regions of the United States. 



Those persons in this country to whom tlie name of trap is not fa- 

 miliar, may still remember the conspicuous ridges, with perpendicular 

 mural fronts, composed of rude columns, Avith sloping backs ; and the 

 isolated peaks and groups that divide the states of Connecticut and 

 Massachusetts almost centrally in two ; commencing in the East and 

 West Rocks at New Haven and terminating on the borders of Ver- 

 mont ; and thus occupying a region which is one hundred and twenty 

 miles long, and varies from three to twenty five miles in diameter. 

 The Pallisados, on the Hudson, are perhaps still more familiar to 

 our domestic tourists ; and it is well known tliat tliey cross the state 

 of New Jersey, from the Hudson towards tlie Delaware. The cave 



* At Red Hill, Lake Winipiseogee, New Hampshire, 

 f In East Haven, two miles from New Haven. 



