EXPLANATION OF THE MAP. 303 



ance which extends south and east through the Union, of which Httle or nothing was said, the 

 proof not appearing in the district in a way which could be made satisfactory to others. The 

 dip or incHnation of the rock to the southwest shows as a consequence a rise to the northeast ; 

 the primary attaining to three times the height, where most raised, to its superimposed rock. 

 From the great denudations which have taken place along Black river, exposing the edges of 

 the rocks from the surface of the primary upwards to the grey sandstone ; from the still 

 greater denudation as to breadth, north of the Helderberg range which descends to the Utica 

 slate, which forms the undisturbed rock of the Mohawk valley, every possible facility is 

 afforded by these enormous excavations, and by those of the north and south valleys, for the 

 examination of the strata of the district. The uplifting of the Primary mass, and the destruc- 

 tion of the whole of the superincumbent masses for some distance firom its centre, enables 

 the examiner rapidly and with certainty to pass from one rock or mass to another, and to give 

 sections of actual contact for the greater number of the different rocks of the whole series. 

 From the partial uplifts having deranged portions of the lower series from the west of Utica 

 east, it is necessary, in order to obtain an uninterrupted succession, to commence to the west 

 of that city. Thus, starting from any point in Lewis county on the Black river, and going 

 southwest to the Coal range of Tonawanda and Blossburgh, the whole of the New- York sys- 

 tem, with some exceptions of the Helderberg division, will, in traversing the intermediate 

 space, appear in succession ; the last of which, the Catskill group, will be seen passing 

 beneath that southern range, being the rock upon which the Coal deposit rests from Bloss- 

 burgh east. 



The whole of the rocks of the district are well illustrated by the two lowest sections upon 

 the map. The first or lowest shows the succession from Ogdensburgh to Blossburgh, and is the 

 most complete as to number of rocks and groups which any section in a straight line through 

 the State could give : it shows the sequence from the primary to the coal. The second sec- 

 tion passes by the gap of Little-Falls, and exhibits an insular appearance of the overlying 

 rocks of the primary at that place, the latter forming the base of the gap. The section com- 

 mences with the Primary at the north, and terminates with the Catskill at the south. 



