BASAL CONGLOMERATR 155 



sioiijilly contains Trenton fossils. It is sometimes represented only by 

 a tew scattered pebbles in the lower beds of the Trenton limestone. 

 Elsewhere it nniy be 30, 50, or even 100 feet in thickness, and the water- 

 worn fragments may exceed even 2 feet in diameter. In such instances 

 lenses of lime " sandstone " occur in the conglomerate, together with thin 

 layers of limestone bearing man}' segments of crinoid stems. In still 

 other localities its constituents are large and angular, showing evidence 

 of accumulation b}'' waves in situ, with practically no transportation. 

 On the weathered surface of such a bed the outlines of the fragments 

 can not readily be seen, and it is not easily distinguished from a jointed 

 and crushed bed of the Kittatinny limestone. Although the maximum 

 observed thickness of this conglomerate is about 100 feet, with neither 

 top nor base exposed, the usual thickness is only a few feet. 



Good exposures are found (1) three-fourths of a mile east of Branch- 

 ville, (2) just north of Newton, (3) at the northeast end of Jenny Jump 

 mountain, near Southtown, (4) a mile east and southeast of Hope, 

 (5) along the road one and a half miles northeast of Hope, and (6) along 

 the railroad one-half mile north of Belvidere. It may be seen also at 

 man}^ other places along the line of the Trenton outcrop, which usually 

 forms a narrow strip between the overlying slate and the Kittatinny 

 limestone. 



Walcott* has described certain conglomerates in the Cambrian lime- 

 stones of Pennsylvania and elsewhere, which he has called intraforma- 

 tional, and which are defined as conglomerates " formed within a geologic 

 formation of material derived from and deposited within that formation." 

 Discontinuous beds of such conglomerates, some of a brecciated nature, 

 have been observed at various points in the Kittatinny limestone, but 

 the beds described above can not be put in that class for the following 

 reasons : 



First. The pebbles are limestone and chert, from the underlying dolo- 

 mitic formation, which is not known to contain fossils of later age than 

 the Calciferous. The matrix, on the contrary, is a much purer lime- 

 stone and contains Trenton fossils (though not abundantly), and the 

 associated limestone layers are very low in magnesia and contain a well 

 marked Trenton fauna. 



Second. The conglomerate rests unconformably on the underlying 

 formation. So far as known the contact is exposed only at the Sarepta 

 quarry, 3 miles northeast of Belvidere, where the conglomerate beds 

 are not strictl}^ conformable to the underlying layers, but dip north- 

 westward at a slightly greater angle. The contact, although not sharply 



* Bulletin 134, U. S. Geol. Survey, pp. 34-40. 

 XX II I— Bull. Geol. Soc. Am.. Vol. 12, 1900 



