334 



BED SANDROCK. 



deposition. The name of oven is given because there is an excavation in the crest of the fold, which with 

 the arch above resembles an old-fashioned oven. 



The dip of the strata sometimes varies greatly in the same hill, when the dip is all in the same direction, 



as at Glebe Hill, in Charlotte. The dolomitic 



FlG - 242 - limestones occupy a lower and more highly 



inclined position than the overlying sandstones. 

 Fig. 242, drawn by Prof. Thompson, illustrates 

 the structure of this hill : b is the dolomite, c the 

 red sandstone, and a is underlying Hudson River 

 slate. Probably the dip of the slates is mostly 

 obscured by metamorphosis, and it is the cleavage 

 planes which are shown upon the section. 

 East of Highgate Springs, near the trilobite locality, there is a singular plication of the strata, which, at 

 the time of our exploration in 1858 we were inclined to regard as a local disturbance. The position of the 

 strata is represented in Fig. 243. The section is well exhibited by the abrupt precipitous termination of 

 several ledges at the south side of a hill. The drawing is a copy of one large ledge fifteen or twenty rods 



Fio. 243. 



Glebe Hill, Charlotte. 



Section of Red Sandrock, in Highgate. 



long. At the east end, the strata dip only 10 E., in conformity with the general position of the terrain. 

 The same strata traced westward, gracefully dip to the west, at first 55, and are then perpendicular- 

 Most of the section has a westerly dip of about 36. At the west end of the ledge the curve is continued 

 so that some of the strata are inverted, and dip to the east beneath older layers. How far this inversion 

 extends to the westward will require further investigation. We thought it to be of limited extent at the 

 time of our observation ; but if it was extended further it would seem to be wonderfully in agreement with 

 the opinion that the red sandrock series is part of the Potsdam sandstone. For if the Potsdam sandstone 

 is inverted at the locality of Fig. 243, the rocks westward should be coarse limestones gradually ascending 

 to the Trenton limestone. Such is the case exactly. The coarse limestones west of the red sandrock 

 would very well agree with the calciferous sandrock, and just east of Highgate Springs there are fossils of 

 the Black River limestone followed by Trenton limestone fossils at the Franklin House. We find a record 

 in our note books of the great lithological similarity of these coarse limestones to the calciferous sandrock. 

 Upon the other view the Hudson River slates ought to be developed between the Springs and the trilobite 

 locality. We could find nothing of the kind in our explorations. We should not wish to believe the view 

 we have just presented of the inversion of the strata without further examination, but mention it as an 

 excellent place to test the value of the different theories. 



Range, Extent and Thickness. 



In New York there is an interrupted belt of Shawangunk grit, occasionally very thick 

 and then reduced to a mere edge, which we suppose to be the southern prolongation of the 

 Vermont range of red sandrock. Their directions and general characteristics coincide. 

 In Vermont it appears first in Orwell and Benson, in one or two hills near their mutual 

 boundary line. It is somewhat uncertain, however, whether the sandstones in Orwell 

 and Benson are anything more than a bed in the clay slates. 



In the south part of Shoreham, at Rich's mills, are the first out croppings of this group 

 of rocks which we have seen at any point north of Benson. The rocks referable to the 



