No. 136.] 



35 



that no separation of their areas is practicable. The great route 

 of travel by Lakes George and Champlain is bordered by cliffs 

 and precipices, in which these rocks are seen in great variety. 

 In this northern region, as well as in the southeastern part of the 

 State, gneiss is exceedingly abundant ; and in some places it 

 appears to change into, or rather to be formed from, sandstone 

 strata, thus exemplifying the belief of most geologists that this 

 is only a changed or metamorphosed condition of other rocks. 



All through these hypogene and metamorphic districts there 

 are many dykes, or perpendicular veins of trap or other igneous 

 rock standing among masses of a different appearance. Not 

 uncommonly a mountain or hill range will show such dykes cut- 

 ting across or through it, miles in distance, and to an unknown 

 depth. These seem to have been merely cracks or clefts by which 

 the country has been riven in many directions, which have been 

 filled by the rise of melted matter from below, just as a crack in 

 a sheet of ice is filled by the underlying waters. They are of all 

 sizes, from half an inch to an hundred feet or more in thickness. 



Except the two great districts above described, the metamor- 

 phic rocks appear only in two or three localities in the Mohawk 

 valley, where they have been uplifted through higher and newer 

 strata. The most conspicuous of these instances has been already 

 mentioned as occurring at Little-falls : it is a ridge which, com- 

 mencing some miles south of the river and crossing it at that 

 point, extends on to the northeastward until it reaches and ter- 

 minates on Lake Champlain near Port Kent, the loftiest of the 

 Adirondack mountains being formed by its highest summits. 



The hypogene and metamorphic rocks generally decompose 

 slowly, and give origin to a poor or barten soil ; and the districts 

 which the coloring on the geological map indicates as formed of 

 these rocks are the least fertile of all our State. 



From the hypogene and metamorphic rocks, we pass to the con- 

 sideration of the stratified fossilbearing rocks. These, in New- 

 York, are among the most ancient of their class, called by the 

 earlier geologists " transition " strata, from the idea that they 

 marked a period of gradual change or progress from what they 

 called the " primary " rocks to what were known as " secondary," 

 the latter term including all strata newer than the Coal. By 

 more modern observers they have been named " palaeozoic," a term 

 signifying " ancient life/' from the fact that they comprise the 



