232 



TRANSITION LIMESTONE. 



fossiliferous groups of De la Beche, and the latter 

 might, with as much propriety, be referred to the 

 lower secondary ir)j.mations as placed in the present 

 group. 



Transition Limesto'i^^^^jsfe have already given a 

 short description of th^ rock (page 82). It is less 

 crystalline than the primxry^ and more so than the 

 secondary, being of an mtt^mediate character be- 

 tween both. It is generally u* a dark gray colour, 

 and sometimes black. This coK^j. owing to car- 

 bon and bitumen disseminated thr^^gii [x,. It often 

 passes into magnesian limestone, frequently 

 contains alumina. It is not rich in nt^tals, though 

 copper is found in it in Virginia. It Cvntains nu- 

 merous fossil organic remains, such as of ^gh and 

 testaceous animals. Of these, the orthoce,^ w^^^ 

 encrinite^ the productus^ the terebratula, and thv ij^i^ 

 lohite\ are the most common. The latter is ol^oj^ 

 met with in the transition limestone at Trentot 

 Falls in this state. The same formation also con- 

 tains numerous coralliform crystallizations. *' The 

 transition limestone," says Professor Renwick, " oc- 

 cupies a narrow belt of very great length in the 

 United States. In North Carolina, Virginia, Mary- 

 land, Pennsylvania, and New- Jersey, it lies in a 

 valley, often diversified by hills of moderate eleva 

 tion, between the first and second ridges of the Ap- 

 palachian group. It enters the State of New- York 

 in Orange county, and follows for a time the course 

 of the Walkill. Thence it passes towards the 

 Hudson River at Newburgli, where it is covered by 

 diluvial gravel, but reappears at the surface on the 

 eastern bank at Fishkill. From thence to Rhine- 

 beck it is wholly confined to the eastern side of the 

 Hudson ; here it again crosses the river, and spreads 

 to a considerable width in the neighbourhood of 

 Kingston and Catskill. At Hudson it occupies both 

 banks of the river, and extends eastward for several 

 miles, but here finally crosses the river. North of 



