86 PECULIAR STRUCTURE OF CLARK.' S CLAY-BEDS. 



merit of precision. In taking specific gravity, results 

 may be obtained which will be accurate to the second 

 place of decimals. The difficulty in reading the scale 

 arising from reflection from the surface of the mirror he 

 has entirely overcome by placing the back of the instru- 

 ment toward the window, and looking- at the scale through 

 a hole one-fourth inch in diameter in a sheet of white 

 card board, held obliquely across the line of sight. 



FEBRUARY 11, 1885— THIRTY-THIRD STATED MEETING. 



Prof. W. B. D wight in the chair ; eleven members and 

 seven guests present. 



The following paper was read : 



THE PECULIAR STRUCTURE OF CLARK'S CLAY-BEDS 

 NEAR NEWBURGH, N. Y. 



BY PROF. W. B. DWIGHT. 



The special clay-beds, whose peculiar features are the 

 subject of this paper, are a part of the enormous deposit 

 of clay and sand formed sj^nchronously over a large 

 part of the Northern United States. This vast deposit, 

 of no small economic value, must not be confounded 

 with the great belt of plastic clays, of far greater 

 economic importance, which crosses New Jersey at the 

 latitude of Trenton, and which feeds one of the noblest 

 industries of that State. 



The plastic clays of New Jersey belong to the earlier 

 cretaceous ; and they supply the more pure and valuable 

 combinations of clay and sand which are among the 

 choicer products of such deposits, such as fire-clays, and 

 stoneware and porcelain clays. But the more northern 

 deposit, which lines the banks of the Hudson River, is 

 much more recent, belonging to the Quaternary age ; 

 and its clays are, in general, fit only for red bricks and 

 tiles. 



70 



