10 GEOLOGY. 



connection would imply would possibly make it necessary to assign 

 to it a marine origin; but the paucity of fossils, and the character of 

 those which are found, are opposed to this suggestion. Furthermore the 

 nature of the series itself } and especially the fact that many of the beds 

 at the borders of the present areas seem to have been deposited near 

 shore, indicates that the strata were never as extensive as their union 

 into a single area would imply. That the several areas of the Newark 

 series have been reduced by erosion is certain from the occasional 

 outliers, but nothing now known proves that their original borders 

 were more than a few miles beyond their present borders. 



South of New Jersey and Pennsylvania, the Newark beds are on 

 the whole less red than to the north, and contain less conglomerate 

 and more carbonaceous matter. 



Subdivisions. — Until recently, the Newark series has not been sub- 

 divided, but it has now been shown that in New Jersey it is divisible 

 into three somewhat distinct formations. 1 Of the lowest {Stockton), 

 arkose sandstone and conglomerate are the most characteristic sorts 

 of rock. A hard black shale (Lockatong) is the most conspicuous part 

 of the middle formation; while red shale and sandstone make up the 

 principal part of the uppermost (Brunswick). This classification has 

 not been extended beyond the State, though the same formations 

 cross the Delaware into Pennsylvania. In Connecticut, also, three 

 main divisions are recognized, 2 and in the Richmond area two. 3 



Igneous rocks associated. — Associated with the sedimentary beds 

 of the Newark series there is much igneous rock. The igneous rock 

 occurs partly in dikes, but chiefly in sheets interbedded with the shales 

 and sandstones. Some of the sheets are extrusive, having been poured 

 out on the surface of the inferior beds and subsequently covered by 

 the superior ones; others are intrusive (sills), having been forced in 

 between the layers of sedimentary rocks after the latter were deposited. 

 In New England, the igneous rocks are mostly extrusive, while in 

 New Jersey the proportion of intrusive sheets is greater. Certain 

 isolated bodies of igneous rock may represent volcanic plugs. The 

 sheets of igneous rock (really diabase, though usually called trap) 

 vary in thickness from a few to several hundred feet. 



1 Kiimmel, Ann. Rept. of the State Geologist of New Jersey, 1896. 



2 Davis, 18th Ann. Rept. U. S. Geol. Surv., Pt. II. 



3 Shaler and Woodworth, 19th Ann. Rept. U. S. Geol. Surv., Pt. II. 



