278 



BASALTIC ROCKS* 



rising in perpendicular height from 20 to 400 feet 

 and below the cascades it passes through a mount- 

 ain of the same more than 1000 feet high, and 

 nearly vertical. 



Extensive basaltic dikes exist in Essex county, 

 in the northern part of the State of New- York, 

 which pursue an easterly and westerly course to a 

 great distance. At Avalanche Lake, a dike eighty 

 feet wide cuts through Mount M'Martin nearly in 

 its centre. Here we perceive on a large scale the 

 effects of frost and water in breaking up the solid 

 crust of the globe ; there being numerous masses 

 of rocks, from 50 to 100 feet long, broken up from 

 their original beds, and carried partly down the de- 

 clivity, constituting a mass of ruins from the base 

 to the summit, which the rains and frost are con- 

 stantly reducing to smaller masses, and urging them 

 onward to mingle with the soil in the plain below. 



What are called the natural walls of North Caro- 

 lina are basaltic dikes, formed of columnar or pris- 

 matic masses, fitting close to each other, and lying 

 with their lengths across the wall, and showing 

 their ends on its sides as in the following sketch. 



Basaltic Dike. 



A trap formation, about three miles in breadth, 

 extends along the Bay of Fundy, in Nova Scotia, 

 a distance of 130 miles. It rises into stupendous 

 precipices, and exhibits basaltic and greenstone col- 

 umns 300 or 400 feet high, against which the waves 

 and tides beat. This range affords a very great 

 abundance of beautiful minerals, such as amethyst, 

 rock crystal, chalcedony, agate, specular iron ore, 



