902 GEOLOGY OF THE THIRD DISTRICT. 



Onondagasalt group, colored of a yellow ochre. This group forms a part of the Helderberg 

 division, being part of the mountain range from Otsego county, to near the Hudson river ; 

 but as it covers a large surface, the geographical rule, which should always have preference 

 in like cases, is adopted. This all important group, as has been before stated, makes a part 

 of the cliff to the east, merely showing its northern outcrop ; but in going west, it constantly 

 presents more and more of its surface, from the superimposed rocks having been removed, 

 which enables it to exhibit a long line of breadth at the west boundary of the district. The 

 part which is composed principally of red shale, Ues to the north generally of the Erie canal, 

 from towards the east end of Madison county, to the east end of Wayne county, being the 

 west limit of the district. 



Helderberg division, with the exception of the Onondaga salt group, in which case the 

 term range is always used : it is colored of a light prussian blue. It forms an uninterrupted 

 range or mountain cliff, from Schoharie county to near Sauquoit creek. From thence west, 

 it is cut down by the many water courses whose discharge is to the north, many of which are 

 wide and deep ; and no correct delineation of the ridge could be made without a correct map, 

 and which must be the result of a topographical survey. 



The Erie division, which consists of the Marcellus shales, the Hamilton group, the Tullt/ 

 limestone, the Genesee slate, and the Portage and Ithaca ' and Chemung groups, constitute 

 two great divisions as to color : the two lower members are represented by very light purple, 

 and the three upper by a light burnt umber. The Genesee slate being unimportant as to 

 surface distribution, is not noticed. 



The Catskill group is of red ochre, and is confined to the counties of Otsego, Chenango, 

 Broome and Tioga. 



From the very small size of the map, it was judged better to confine it entirely to the 

 representation of the rock masses of the State, leaving out the whole of the quaternary pro- 

 ducts ; the insertion of which would have made it so complicated, as to be useless to all but 

 those already well acquainted with the subject. Unless a map is upon a large scale, it is not 

 practical to combine the two, without greatly imparing the value of the part which pertains to 

 the rock masses. Where the greatest gain is desired, the rock masses and the quaternary 

 products should be laid down upon separate maps. It is the intention of those engaged in 

 the Survey, to place a large map of the State in the Geological room in Albany, showing both 

 the rocks and the quaternary products. 



The Third District is an important one, for it contains the whole series of rocks, from the 

 Primary to the Catskill group, with some exceptions. The first are those which relate to the 

 Taconic system, of which the district gives no hght ; the second and last is the Schoharie 

 grit, which probably is wanting, not having been seen in place. With the exceptions of par- 

 tial uplifts of the Mohawk and its north vicinity, the whole of the rocks of the district are 

 relatively undisturbed, exhibiting a general dip to the southwest, the entire mass of the rocks 

 of the New- York system inclining from the primary nucleus. There are imdulations, no 

 doubt, in the great mass to the south of the Mohawk, forming a part of a system of disturb- 



