RELATIONS OF THE TACONIC SYSTEM. 55 



occasions arise from having placed too much reliance upon lithological characters, which 

 it must bo admitted are remarkably similar to those of the Hudson river shales, and the 

 primary schists. Thus upon the east, in the range of Graylock, are those slates which have 

 usually been denominated tahose, and sometimes mica slates. If lithological characters 

 alone are relied upon for determining their age and position in the series, some geologists 

 might place them in the Primary ; and then again those upon the west, in the vicinity of 

 Hudson river, might, without doing violence to the same characters, be placed with the 

 slates and shales of the Champlain division. On the principle of giving to the Champlain 

 division those rocks which resembled its own members, and to the Primary system a similar 

 title, we might divide the Taconic system into two great divisions according to their resj)ec- 

 tive lithological characters. Such a division, however, can Ijy no means be admitted, for 

 reasons which will be stated hereafter. I may state, however, that geologists, by allowing 

 too much importance to lithological characters, have overlooked the Taconic system. In 

 this connection, too, I may remark, that it is important, when it is wished to determine 

 the amount of alteration which a mass has suffered, to ascertain its origin, or from whence 

 its materials were derived ; and also that it will be rarely essential to prove, or admit, that 

 it has been exposed to an intense heat ; for steam, or hot water charged with silex or 

 other soluble bodies, are competent to produce great changes in a mass. Thus in the 

 Cumberland coal-field of Rliode-Island, the coal is traversed by seams or veins of quartz, 

 veins which we do not feel disposed to admit were injected in a state of igneous fusion, but 

 were rather deposited from a vapor or water holding silex in solution. 



I shall take the broad and distinct ground that the Taconic system occupies a position 

 inferior to the Champlain division of the New-York system, or the lower division of the 

 Siliuian system of Mr. Murchison. In order to prove that this position is well chosen, it 

 will be necessary to refer the reader to localities where one system of rocks reposes upon 

 the other ; and that I might set this beyond the possibility of a doubt, I have sought those 

 points where the slates of the Taconic system come in contact with the lower limestones, 

 or with the Potsdam sandstone of the New- York system. 



With these objects in view, I commenced my examination at Whitehall. This I consi- 

 dered a favorable place for the exhibition of the fact sought, since here the Utica slate and 

 Hudson river rocks are wanting. The New- York series commences with the Potsdam 

 sandstone, which rests on gneiss, and extends upwards so as to embrace merely the Calci- 

 ferous sandrock, and perhaps a very small remnant of the Chazy limestone. The rocks 

 dip eastwardly at an angle ranging from 2^° to 5°. On being traced in the direction of dip 

 along the sides of the uplift, they were found to extend two and a half to three miles only 

 from the lake, and to attenuate rather rapidly ; so much so, that they are cut through in 

 several places, leaving the easterly portions separated from the great mass at the west. In 

 these deep cuts the Taconic slate is denuded, and exposed in its steep southeasterly dip. 

 More than this, the immediate line of contact is exposed at one of the ravines in rear of 



