232 



TRANSITION LIMESTONE. 



fossiliferous groups of De la Beehe, and the latter 

 might, with as much propriety, be referred to the 

 lower secondary formations as placed in the present 

 group. 



Transition Limestone. — We have already given a 

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

 crystalline than the primary, and more so than the 

 secondary, being of an intermediate character be- 

 tween both. It is generally of a dark gray colour, 

 and sometimes black. This colour is owing to car- 

 bon and bitumen disseminated through it. It often 

 passes into magnesian limestone, and frequently 

 contains alumina. It is not rich in metals, though 

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

 merous fossil organic remains, such as of fish, and 

 testaceous animals. Of these, the orthocera, the 

 encrinite, the productus, the terebratula, and the tri- 

 lobite, are the most common. The latter is often 

 met with in the transition limestone at Trenton 

 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 Nevvburgh, 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 



