302 UTICA SLATE. 



1. Black calcareous slate. 2. Thin beds of limestone, containing nodules of pyrites. 

 3. Glazed shales, having an anthracitous lustre. 



The common variety greatly resembles the shales of the Trenton limestone ; differing 

 from them principally by being firmer, and exhibiting a double system of joints, which 

 are often filled with seams and veins of calcite. The common variety can be seen at any 

 exposure of the formation, from Canada to New York. The second variety is best 

 exhibited upon the islands in Lake Champlain. The limestone beds are rarely more 

 than six inches in thickness, and generally are from one to three inches thick. The 

 nodules of iron pyrites greatly resemble fossils, and in many cases are doubtless altered 

 organic remains. They can be found at almost any ledge of this rock, in North Hero, 

 and in the east parts of Grand Isle and South Hero. In the Cabinet, Nos. ^ to ~^ are 

 specimens of these nodules of pyrites. 



The veins of calcite constitute a marked feature of this rock. There are three varieties 

 of them : the large veins or dikes ; the smaller ones, that twist and branch in every 

 direction frequently like the branches of a tree ; and thirdly, those small veins that occupy 

 the cleavage seams, and are parallel to one another over large areas. 



The first class are numerous in the north part of Grand Isle, near Mr. Hurlburt's house. 

 The largest is two feet wide. They cross the strata at almost every angle more 

 usually crossing at right angles to both dip and strike and have disturbed the original 

 position of the strata in their immediate vicinity. The substance of the veins is pure 

 white calcite. The second kind of veins is exceedingly abundant upon most of the islands 

 in the north part of Lake Champlain. We would specify the southwest part of North 

 Hero as a locality particularly abounding with them. For half a mile, along a cliff 

 twenty-five feet high, these white veins show themselves, ramifying among, crossing or 

 running along with the strata, and occasionally interrupted by veins of a newer age, 

 crossing them per force. In many seams, the calcite had been pressed by dislocation so 

 much that it was smoothed, and the glazed surfaces resembles the slickensides of metallic 

 veins. A fine locality of the third variety (which is perhaps Hudson River slate) is in 

 the cliff on the lake shore, in the northwest part of St. Albans. Several rods square 

 have these veins parallel to one another, and instantly attract the attention of the passer 

 by, because of their beauty. 



Divisional Planes. 



The most conspicuous divisional planes in the Utica slate are those of cleavage, and these are generally 

 inclined at a high angle. Jointed planes occur, but we have measured none of them, and cannot say what 

 their general position is. 



Sometimes the cleavage planes are so prominent that the attention of the observer is entirely occupied 

 with them, to the neglect of the planes of stratification; and again the planes of stratification have entirely 

 disappeared. A metamorphic action, adequate to produce an incipient crystallization, would totally 

 obliterate the planes of the strata. We give a list of the positions of the cleavage planes observed in the 

 Utica slate: 



Locality. Strike. Dip. Observer. 



Shoreham, west part, N. 10 E., 45 E., A. D. H. and C. H. H. 



Bridport, southwest part, N. 66 E., 29 E., C. H. H. 



Addison, Cobble Hill, N. 20 E., 75 E., C. H. H. and A. D. H. 



