CHAMPLAIN DIVISION. 123 



^ 5. ISLE-LAMOTTE MARBLE. 



Reposing upon the hirdseye, is a black finely granular limestone, called the scvm-foot 

 Ikr by the quarrymen at Watertown in Jefferson county, but which is better known in 

 market as the Isle-Lamotte marble. At the latter place, it is twenty-five or thirty feet thick ; 

 while at Watertown it is only seven or eight, and being at the same time lumpy, is unfit 

 for marble, or any use except for the coarsest structures. At Glensfalls it is nearly as im- 

 portant as at Isle Lamotte. When present, it intervenes between the birdseye and trenton : 

 into the latter it gradually passes. The fossils of the trenton are never, or very rarely 

 found in it, and then only in the superior layers : neither do those of the birdseye pass 

 upward into the Isle-Lamotte marble. It seems to he constituted of one or two thick beds, 

 as if it had been deposited with great rapidity. 



^ 6. Trenton limestone.. 



The Calciferous sandstone and the Trenton limestone constitute the two important lime- 

 stones of this division ; inasmuch as they form continuous masses, and far more extensive 

 than all the other limestones put together. It may be described under three varieties : 1, 

 it is a rock made up of alternating layers of limestone and black slate, as at Chazy ; 2, of 

 a thick mass of black limestone, as at Trenton falls ; 3, a gray limestone, sparkling from 

 crystallization. These varieties sometimes exist together, and sometimes they are sepa- 

 rated ; and, besides, where all are present, their relative position is not constant. At 

 Montreal, the gray variety is the inferior mass ; at Watertown, it is the superior. But 

 though there is irregularity in the position of the varieties, there is much constancy in the 

 kind of fossils which belong to the rock. The upper part of the rock is a black calcareous 

 slate, and passes by imperceptible gradations into the succeeding slate. Sometimes, the 

 rock consists of alternating layers of black fine-grained slate : this is the case at Chazy, 

 where it is between four and five hundred feet thick. 



§ 7. Utica slate. 



We propose to retain the divisions and names which were adopted in the Geological 

 Reports, although some of them have but a slight claim to the distinction of independent 

 rocks. This is the case with the Utica slate. It would do no violence to geological classi- 

 fication, to incorporate it with the slate of the Trenton limestone below, or with the Loraine 

 shales above. It is an intermediate deposite ; or, in other words, a transitional formation, 

 connecting the two ; on the one hand, it departs from the typical mass of the limestone, 

 and becomes merged by gradual approximations with the Loraine shales. The fossils 

 partake more of the character of the shales, than of the limestone. 



This slate has no distinctive character in its composition, by which it may be known 



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