Connecticut River Valley. 925 
extends into West Springfield, Westfield, and Southwick, Ms. and in 
Connecticut forms the Talcott mountain, Farmington, Meriden, and 
Southington mountains, and having a number of subordinate parts, 
and parallel ranges, terminates at East and West rock in New Haven. 
| Rests upon secondary.—The hills and mountains of trap rock are 
spread over and rest upon the top of the secondary formation, as may 
be seen at several places, and at none more distinctly and extensive- 
ly than at Rocky Hill, three miles south west of Hartford. Similar 
rocks are found in New Jersey, and other places in the United States, 
and their usual position, in relation to rocks formed by subsidence in 
water, is to overlie and rest uponthem. ‘That the trap rock hills and 
mountains were formed, or placed in their present position, after the 
formation of the secondary strata, is as certain as that the latter were 
arranged and deposited in water. By what natural agents and modes 
of action could the trap rocks have been elevated, and placed upon 
the previously formed beds of sandstone, or clay rock? 
Of igneous formation.—It has been extensively maintained by ob- 
servers of the structure of rocks, that trap, or greenstone, is a product 
of fusion. Recent observations render it almost certain that some 
trap ranges have been produced by the melting and hardening of other 
rocks. ‘Ihe appearance of the trap and sandstone, several feet above 
and below their junction, is different from the appearance of the 
same rocks at a greater distance. ‘The color and texture both appear 
to have been changed, as might be anticipated from the placing of 
highly heated or melted rock upon strata which were cold. ‘The ap- 
pearances of both rocks have been described minutely, by Professor 
Silliman, in the American Journal of Science, for Oct. 1829. He 
considers the proofs conclusive, that the greenstone of the Connec- 
ticut river valley, has hardened into its present state, from a previous 
state of fusion. ‘To remove all doubt that trap rock has been pro- 
duced by the fusion of other rocks, it has been observed in volcanic 
regions, that what is lava at the surface gradually changes below, 
until the difference between undoubted lava and trap vanishes. 
Dykes.—Trap rocks are found in many parts of Europe and Amer- 
ica. Besides their more general position, resting upon other rocks, 
they are found penetrating the earth and solid strata, in veins or dykes, 
to an unknown depth. Portions of greenstone dykes, disclosed by ex- 
cavation, have repeatedly been mistaken for artificial walls, and when 
traced to a considerable extent have excited wonder and astonish- 
ment, before the nature of the formation was understood. Such 
