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the Musconetcong Mountain. Following tiie soutliern edge of 

 this narrow belt for about six miles, it finally quits the State by 

 crossing the Delaware river, near the mouth of Gallows run. 



Comj)osition and Structure. — While the prevailing and dis- 

 tinctive rocks of this formation are a dark brownish-red sand- 

 stone, and a soft and friable argillaceous red shale, it presents a 

 considerable diversity, especially among its lower beds, both as 

 respects its aspect and composition. In some parts of the series, 

 we find the argillaceous matter so predominant, that certain beds 

 assume almost the character of a homogeneous consolidated clay, 

 of a brown or dark purple colour, in which the laminations are 

 hardly discernable. On the other hand, the rock is not unfre- 

 quently composed mainly of sand, cohering into a true arenaceous 

 sandstone, by a slight amount of clay, usually red, but sometimes 

 white. In these cases it often contains a notable quantity of 

 mica, and is then a red flaggy sandstone, easily divisible in the 

 plane of stratification. In the inferior part of the formation, 

 beds of rather coarse and heterogeneous sandstone passing into 

 conglomerate, are not unusual. But the pebbles rarely make up 

 the chief part of the mass, and the larger kinds are somewhat 

 sparsely scattered, in the midst of what ought rather to be 

 termed a coarse and angular sand. The materials of these beds 

 seem to indicate a derivation from the contiguous primary 

 rocks, southeast of the formation, consisting principally of rather 

 angular grains of quartz and felspar, the latter most usually 

 passing by decomposition into clay or kaolin, together with a 

 less proportion of mica, and a little of the red argillaceous matter 

 so predominant in the formation. We sometimes find in the 

 coarse conglomerates, besides the abraded fragments of the 

 primary rocks, flattish pebbles of the red shale, which give to the 

 rock a rather mottled aspect. 



An accurate conception of the diversified contents of this 

 extensive formation will be best conveyed by a somewhat 

 detailed description of its several portions, as they are exposed 

 along a section transverse to the strike of the beds. I shall 

 select the district bordering on the Delaware river, where the 

 series is more entire and better developed than in any other 

 tract of the State, and treat of each natural division in succession 

 as it presents itself in the ascending order. Commencing, there- 



