106 



been discovered here, are yet current among those ignorant of 

 the subject. 



Fbssiliferous Limestone of the Delaicare, Formation VIII. 



Geographical Range. — Resting conformably above the forma- 

 tion last described, there occurs an interesting and important 

 rock, the uppermost of the older secondary strata embraced 

 within the limits of the State. It is a blue fussiliferous limestone, 

 occupying, if we adhere to a simple classification of the strata, a 

 position near the bottom of the eighth formation of the series. Its 

 dip is invariably towards the west-northwest, at an angle averag- 

 ing about 30°. 



This rock enters the State at Carpenter's Point, whence it ex- 

 tends in the form of a rather steep ridge, parallel with the general 

 course of the Delaware to the Wallpack Bend, where it crosses 

 the river into Pennsylvania. This ridge has the valley of the 

 Flatkill at its southeastern base, for nearly its whole length, 

 bounding which, it forms in many places a rather steep escarp- 

 ment. Between its northwestern base and the river, there usually 

 extends a narrow diluvial plain, in one or more low terraces, 

 forming the beautiful and fertile flats of the Delaware. 



The rock appears to increase in thickness as we trace it north- 

 eastward from the Wallpack Bend. In fact it only begins to de- 

 velope itself as a separate member in the series of our strata, be- 

 tween the Wind Gap and the Delaware Water Gap in Pennsylvania. 

 This expansion, conjoined with a gradual reduction in the angle 

 of its dip as we advance towards Carpenter's Point, causes the 

 stratum to occupy, in the vicinity of Milford, a considerable 

 breadth. This is the same rock which forms the chain of the 

 Helderberg hills, west of Albany, in New York. 



Composition and Structure. — The prevailing aspect of this rock 

 is that of a rather pure blue limestone, embracing the two leading 

 varieties, that consisting of the carbonate of lime alone, and that 

 in which the carbonate of magnesia also forms an important 

 part. It has usually a fine close grain, a smooth fracture, and a 

 clear bluish or bluish-gray colour ; other portions of it, however, 

 depart from these characters, being sometimes of an argillaceous 

 and earthy texture, sometimes sparry or subcrystalline, and some- 



