EXPLANATION OK THE PLATES. 367 



PLATE XX. 



The middle section, or seclion 1 of Plato 20 and 21, is an east and west section, and extends from the 

 Hudson to Lewiston. Although not drawn in a direction perpendicular to the strike of the rocks, 

 yet it shows very satisfactorily the thinning out of the strata as they extend westward from the 

 Helderberg range. The Ontario division here is absent, while the Heldcrberg is supposed to be 

 fully represented. Westward, and near Little falls, the Ontario division again appears. At the 

 eastern extremity of the section the Helderberg and Erie divisions are prominently exhibited. In 

 the central counties, the Salt group forms the superior mass ; while at the extreme west, the Ontario 

 division occupies the surface. 



Section 2, Plate 20, exhibits the position and succession of rocks at Schoharie. This section is de- 

 signed also to illustrate the fact tliat the valley was formed by denudation. 



Section 3. The High falls of Rondoiit, in Ulster county, show a singular derangement of the strata, 

 which resulted in fracturing them at least three times in a very short distance. The river falls 

 over a rock which seems to be equivalent to the pentamerus limestone, or a mixture of this with 

 the delthyris shaly limestone. 



Section 4. The Limestone creek, at JManlius, passes through a gorge and over a ledge of limestone. 

 The superior rock, or that which forms the hills on the east and west side of the village, is the 

 Marcellus slate. 



Sections 5 «fc 6. Exhibit remarkable flexures of the strata. Arches, curves and fractures are constantly 

 recurring between Catskill and Leeds. West of Leeds, the rocks are only slightly disturbed. 

 The best route for observing the numerous changes of dip, etc., is the old railroad between the 

 above named places. 



PLATE XXL 



Section L Is a continuation of section 1 upon Plate 20. 



Section 2. The uninterrupted succession of the lower sedimentary rocks of the New- York system, on 

 a north and south line beginning at Theresa and terminating at Auburn, is a very satisfactory 

 exhibition of stratigraphical succession. It exhibits the relative position of the Ontario division. 



Section 3. The turnpike route from Catskill to Gilboa exhibits the great scale upon which the Catskill 

 division is developed in New- York. The superior mass of the Catskill mountains is undoubtedly 

 the conglomerate of the Carboniferous series or system : it is colored purple. 



Section 4. This section follows up a creek which falls into the Cayuga lake at Auburn; the regular 

 succession only is intended to be indicated. 



Section 5. This section runs north and south, and is intended to exhibit the succession of rocks upon 

 Cayuga lake. 



