564 



Report of the State Geologist. 



not been observed here, nor in any of the anorthosite in the county. As was 

 to be expected from the less complete granulation, but little of the rock is 

 foliated, the basic minerals occurring in clumps rather than in streaks. 



A short distance up the hill from the turnpike, a well foliated gabbro 

 outcrops. Owing to the tangle of brush arid the thin soil covering, its extent 

 could not be determined, but it is not great. It is less basic than the ophitic 

 gabbros, and lacks that structure; neither have the uncrushed labradorites 

 the abundant inclusions which characterize those of the ophitic gabbro. 

 Besides the labradorite the rock contains much garnet and magnetite, consid- 

 erable apatite, and what was probably augite now wholly passed into chlorite. 

 Granulation is not complete. The labradorite crystals which have partially 

 escaped this process, show beautiful polysvnthetic twinning, and exhibit most 

 notably effects of the dynamic action other than the granulation. Not 

 only are they broken and the fragments displaced, but nearly all are bent, 

 the bending being most clearly brought out by means of the oft-repeated 

 twinning, as shown -in the accompanying figure drawn with the camera lucida. 



Broken and bent labradorite crystal from gabbro on Rand bill, Altona. Tbe surrounding- granular 



material i» almost wholly labradorite. 



Series IV. With the exception of the small areas just noted, the Pots- 

 dam sandstone is the surface rock throughout the township. Moreover, here 

 is by far the most impressive display of this rock to be seen in the county, 

 if not in the state. Extending north from Rand hill is a plateau of nearly 

 horizontal Potsdam sandstone, running up to heights of 1,100, 1,'20<>, and 

 even 1,500 feet, and stretching away northward with an average fall in level 

 of from seventy-five to one hundred feet per mile. For the most part it is 

 very bare of debris, and on the steeper slopes the naked ledges of stone rise 

 in a series of gigantic steps, as if they had been swept bare of debris 

 by powerful currents. The district goes under the name of the "Flat 

 rocks." It is rather deeply incised by the Great Chazy river but otherwise 

 is not deeply dissected by erosion, appearing as a base level of tolerably 

 recent elevation. Rand hill is a monadnock rising above this level. 



