THE NEWARK ROCKS 41 



Solitary grains and crystals of titanite occur and frequent masses 

 of calcite were observed. The lime-silicate hornfels effervesces 

 with acid. Their occurrence here indicates a deep-seated origin 

 for the Palisade sill. 



The association of the slate hornfels and the lime-silicate 

 hornfels is extremely interesting. The former makes up the 

 main mass of the altered beds. The lime-silicate hornfels forms 

 in most cases small layers in the slate hornfels, the thickness of 

 the former often being no greater than that of a sheet of paper. 

 These layers are parallel to each other and to the original strati- 

 fication of the shales. Frequently they form small elliptical 

 masses, joining each other like a string of pearls in the stratifica- 

 tion plane. From this it is but a step to rocks in which the lime- 

 silicate hornfels form only roundish eyes and knots in the hard, 

 black slate, the "incipient segregation," which gives the rock a 

 mottled appearance. In still other cases the lime-silicate horn- 

 fels traverses the darker hornfels in veins and bands at various 

 angles to the stratification. Before metamorphism these were 

 probably veins of calcite, which, together with the surrounding 

 shales were altered on the intrusion of the trap. 



In all these various relations the boundaries of these two 

 rocks, of such different chemical composition, are sharply 

 marked, both to the naked eye and microscopically. This is 

 strong evidence that during the metamorphism these rocks were 

 not molten, but that the changes occurred in solid, or at most, 

 very slightly plastic beds. The authors conclude that the beds 

 were originally argillaceous shales, locally strongly calcareous 

 and traversed by veins of calcite and interbedded with layers of 

 arkose sandstone. They find in the contact phenomena strong 

 evidence that the trap was intrusive and cooled at great depths. 



Metamorphosed shale, in every respect identical with these 

 rocks, so far as macroscopical examination can determine, occurs 

 along the Rocky Hill ridge, and is well shown along the canal 

 near Rocky Hill village. Epidote and tourmaline-bearing 

 shales occur on both sides of the Sourland Mountain trap, and 

 are well exposed at Lambertville, where many of the features 



