138 GEOLOGY OF THE SECOND DISTRICT. 



Taconic System not connected with or related to the Slates and Shales of the Champlain 



Group. 



Much difficulty is encountered, as has already been hinted, when we attempt to draw the 

 line of demarkation between the shales and slates east of the Hudson river and Lake Cham- 

 plain, and the slates of the Taconic system. So nearly do the latter resemble the former in 

 lithological characters, that in specimens of small size, the one might be mistaken for the 

 other. But this is a common difficulty, or one common to all rocks of the same lithological 

 characters, and it is not to be considered as a positive objection to the separation which I now 

 propose. 



There arc two or three other points it may be well to state in this place : One is in regard to 

 tiie condition of the country along the line of junction of these, and of almost all other rocks ; 

 there is, for example, a concealment of the strata by rocks and earth for quite a wide space, 

 covering the termination of the masses on either side ; added to this difficulty is the confusion 

 created by the great sameness in the direction of dip ; and as both are lithologically slates or 

 shales, and both liable to certain changes in their planes of stratification and of deposition, a 

 wide door is opened through which we may run into mistakes and create confusion. In fact, 

 it often happens that where either of these difficulties exist alone, special care has to be taken 

 to avoid error ; but where they all appear, as in the instance imder consideration, we can 

 scarcely e.xpect to escape falling into some gross mistake — that especially which concerns 

 the designation of the rock. 



But I have, at the head of this section, asserted that the slates and masses of the Taconic 

 system are not related to, or connected with, those of the Champlain group. By this I mean 

 that tliey are not the same rocks in another condition ; or, in other words, they are not a part 

 of the former group in a metamorphic state. This is proved by the want of conformity in 

 all essential characters, particularly the want of similarity in position of those rocks which 

 agree in chemical constitution. We do not expect that by any agent a slate can be changed 

 into a hmestone, or is likely to be ; neither will the order of superposition in the series be 

 changed by metamorphism. Hence, in rocks suspected to be metamorphic, it is necessary to 

 ascertain the order of the masses ; and if the order corresponds, and there is a gradual change 

 from one to the other, it is possible that one of the masses is metamorphic ; but if there is no 

 correspondence in the position of the masses composing the group, then we have no right to 

 call in the aid of the metamorphic theory to prove that the rocks belong to one group or era. 

 Thus, in the limestones of tiie Taconic system, we have no correspondence in position wdth 

 either of the limestones of the Champlain group. The granular quartz, too, if it is equivalent to 

 any mass in this group, it is to the Potsdam sandstone ; but it lies between masses of lime- 

 stone, and is in the form of great beds unconnected with each other. It is, therefore, the 

 want of similarity in the position of the masses with the rocks lying west, etc. which they 

 resemble sometimes so closely, that leads me to reject the idea that the rocks of the Taconic 

 system are merely metamorphic rocks or altered masses of the Champlain group. But if this 



