26 H. B. KUMMEL 



purple argillites ; (c) dark gray and green flagstones ; (d) dark 

 red shales approaching a flagstone ; (V) and occasional thin 

 layers of highly calcareous shales. There are all gradations 

 between these somewhat distinct types, so that the varieties of 

 individual beds are almost countless. Both ripple-marks and 

 mud-cracks occur at all horizons, showing that shallow water 

 conditions prevailed throughout the time of their deposition. 

 On the other hand, the absence of strong currents or violent 

 shore action is indicated by the extreme fineness of the material. 



The Lockatong beds are ridge makers, owing to their supe- 

 rior hardness and consequent resistance to the agents of degra- 

 dation. In this particular they are surpassed only by the trap 

 rocks. Sourland Mountain is composed largely of these rocks, 

 although its backbone is formed by the outcropping edge of a 

 trap sill. The high plateau in Hunterdon county, between Flem- 

 ington and Frenchtown, which rises 300 to 500 feet above the 

 adjoining region, is due also in large measure to the comparative 

 indestructibility of these hard argillites and flags. They give 

 rise to a rather heavy wet clay soil, often swampy unless arti- 

 ficially drained. The surface is quite thickly strewn with slabs 

 of argillite and flagstone and on the steeper slopes rock out- 

 crops are generally abundant. 



The Brunswick beds. — In general this group consists of a 

 monotonous succession of very soft argillaceous red shales 

 which crumble readily to minute fragments, or split into thin 

 flakes. Much of it is porous, the minute, irregular-shaped cavi- 

 ties being often partially filled with a calcareous powder. Cal- 

 cite veins and crystals are common in some layers. Locally 

 lenticular masses of green shale occur in the red. In size these 

 range up to a foot or two in diameter, and vary in shape from 

 nearly spherical to lenticular masses, narrowing down to thin 

 sheets along cracks. They are undoubtedly due to chemical 

 changes resulting in the leaching of the shale. 



Although the majority of this series are soft red shales, 

 there are some hard layers, chiefly near the base, and occasional 

 beds of fine-grained sandstone and flagstones, some of which 



