ONONDAGA-SALT GROUP. 153 



III. HELDERBERG DIVISION. 



Remarks descriptive of the appearance of the Helderberg range from the hills east of 

 Greenbush, and explanatory of Plate I. — This range is remarkable for the succession of ter- 

 races as it rises from its eastern slope, and for the offsets after it has attained its height 

 towards the north or valley of the Mohawk. Each terrace marks the position of the 

 several limestones, which, being harder than the shales, form permanent tables extending 

 beyond the limits of the shales, that are confined to an outcropping and nearly horizontal 

 edge. The slope or dip is southwest, and the range rises from beneath the Catskill moun- 

 tains, which rise up in dome-shaped segments upon the left. We see, in this view, merely 

 the eastern slope : to the west there is a succession of minor ranges, separated from each 

 other by north and south valleys. The Hudson-river series appears in the foreground, 

 and are colored purple ; the limestones are colored blue, the shales a light drab, and the 

 Catskill sandstones (which are the superior rocks, and beneath which all disappear) a light 

 brown. 



§ 1. Onondaga-salt group. 



If we estimate the importance of a group or series of rocks by the amount of useful 

 materials it furnishes, then this group is certainly one of considerable consequence. This 

 will be admitted, probably, when it is stated that it furnishes most, if not all the plaster 

 used in Western New- York, and much that is used in the New-England States. It un- 

 doubtedly gives origin to the brine springs from which a large proportion of our salt is 

 made, and from which an immense revenue is derived by the State. Besides these im- 

 portant considerations, the rocks themselves form by decomposition an excellent soil, and 

 the belt over which the group prevails is one of the best agricultural districts in the State 

 of New-York. Without doubt, then, if this view is the true one, this group becomes both 

 geologically and economically important. Its relations and associations are inquiries of 

 considerable moment ; for it is essential that its position in the series should be well un- 

 derstood, and the nature of the deposits forming it well determined. Such being our 

 opinion in regard to it, we proceed to describe the series in the same order which has been 

 observed in the preceding groups. 



The specif c characters which distinguish this group from the preceding, and the different 

 members which form it. Leaving out of view those characters which are derived from its 

 organic remains, we find that it is composed in the ascending order, of, 



1. A red shaly fissile mass with green spots and a few bands, constantly breaking down under the 



action of atmospheric agents. 



2. Green shale, rather massive, in which plaster beds are embraced, and which also contain casts of 



crystals of hopper-shaped cavities in which common salt once existed. 



[Agricultural Report,] 20 



