AGE OP WHITE LIMESTONE OF SUSSEX COUNTY. 397 



T\\e second paper was entitled — 



AGE OF THE WHITE LIMESTONE OF SUSSEX COUNTY, NEW JERSEY 

 BY J. E. WOLFF AND ALFRED H. BROOKS 



[Abstract] 



The paper first reviewed the work and opinions of previous observers, which have 

 mainly tended to either of two views, namely, that the white limestone is of pre- 

 Cambrian age or that it is identical with the Cambrian blue limestone of the re- 

 gion, the present crystalline condition being due to the action of igneous rocks, 

 perhaps assisted by regional metamorphism. In that connection the authors ex- 

 pressed their debt to the previous work of F. L. Nason, which all who visit the 

 region mast appreciate, whether or not they agree with his conclusions. 



A description was then given of the detailed work, on which the conclusions of 

 the present paper rest, illustrated by maps, cross-sections, and specimens. The 

 new features of these observations were first the evidence for several faults in the 

 field, two of especial importance being along the line of contact of the white and 

 blue limestone, and, second, the description of a new quarry in the white lime- 

 stone at Franklin, where the overlying Cambrian arkose has filled a deep crevice 

 in the white limestone, and contains large fragments of that rock and pieces of 

 mica, feldspar, and quartz characteristic of the white limestone, granite, and asso- 

 ciated rocks, affording absolute proof of the pre-Cambrian age of the white lime- 

 stone, and also an explanation of the apparent interbedding of the two rocks ob- 

 served elsewhere. The results were summarized as follows: 



Where there is not faulting, the sandstone lies between the blue limestone and 

 the white limestone or gneiss, and is everywhere derived from the gneiss, the 

 granite, or the white limestone, containing fragments of all three rocks. The blue 

 limestone and sandstone are unconformable in dip to the foliation of the other 

 rocks except along fault lines. The strike may or may not coincide. The white 

 limestone has generally the same strike and dip of foliation as that of the gneisses, 

 and the pitch structure of the latter is conformable in direction and amount to the 

 pitch of the ore bodies of the white limestone. The granite nowhere cuts the blue 

 limestone or sandstone, but cuts the white limestone and gneisses indiscrimi- 

 nately. The sandstone has in one place distinctly filled a crevice in the white 

 limestone from above, containing boulders of the limestone and fragments of the 

 characteristic minerals of this and the other rocks. The apparent transitions be- 

 tween the two limestones are explained as the result of fault brecciation and shear- 

 ing, the apparent interbedding of the white limestone with the quartzite, as the 

 result of the filling of preexisting fissures or cavities in the white limestone, often 

 complicated by faulting. Since the white limestone is an integral part of the 

 gneissic formation and of contemporaneous formation, and the granite which is 

 eruptive through both is of later origin, coming after the formation of the charac- 

 teristic structures of foliation and pitch, it seems necessary to ascribe the present 

 mineral composition of the limestone and ore bodies to causes not necessarily con- 

 nected with the intrusion of the granite, however much that may have acted 

 locally. 



The paper was discussed by B. K. Emerson, J. F. Kemp, and J. E. Wolff. 



At 12.45 p m the section adjourned for lunch. 



