96 NEW YORK STATE MUSEUM 



races can be identified. They are relics of the postglaoial Lake 

 Vermont, the expanded predecessor of Lake Champlain as estab- 

 lished by J. B. Woodworty to whose work, and that of C. E. Peet, 

 reference must be made for the interpretation of these phenomena 

 as bearing on a wide area. The object, here in view, is rather to 

 -give to the reader a bird's-eye view of the region under discussion. 



As to the thickness of the clays no very definite data has been 

 obtained. Gulches cut them to a depth of 20 or 30 feet and the 

 clays obviously go lower. In the Ticonderoga quadrangle on the 

 south and in the northern portion of the town of the same name, 

 brooks have eroded downward through fully 100 feet of clay. The 

 depth is doubtless somewhat governed by the relief of the bed rock 

 left on the retreat of the ice sheet. 



Water-sorted sands are very much in evidence a mile or less west 

 of Port Henry where Mill brook crosses the railway to Mineville. 

 Very thick and extensive beds in the nature of delta sands have 

 gathered fro'm the 600 to below the 500 foot contour. They seem 

 to have either been deposited against a lobe of ice which still filled 

 the valley below, or else to mark a delta formed at a time when the 

 waters stood at this level. The sands are deeply trenched by Mill 

 brook and at periods of flood sufifer severely. The present dam and 

 pond used by the electric company have obliterated some of the 

 exposures which were pronounced in former years. 



Sands with more or less fine gravel appear in the Schroon valley 

 and likewise in the valley of the Boquet river. The dunes of the 

 latter have been mentioned in the opening pages as have also the 

 deltas and lake bottoms. The correlation of the deltas would re- 

 quire more detailed study than has been given while working over 

 the hard geology. 



Chapter 10 



ECONOMIC GEOLOGY 



The chief of the mineral resources of the area here discussed is 

 iron ore. Attendant upon the smelting of the products of the 

 mines, limestone quarries have been opened in both the Grenville 

 and the Beekmantown formations to supply the necessary flux. 

 Some subordinate quarrying has also been done upon the serpen- 

 tinous limestones of the Grenville for ornamental stone. There are 

 besides these, great reserves of clay for the manufacture of brick 



1 Ancient Water Levels of the Champlain and Hudson Valley. N. Y, 

 State Mus. Bui. 84. 1905. p. 190. See alsr the discussion by C. E. Peet. 

 Jour. Geol. July-August 1904. p. 458. 



