1885.1 &<'* IFrazer. 



and their frequency throughout the middle belt of limestone and schists, 

 would lead one to conclude either that the seats of the igneous action 

 resided within the beds of the newer rocks, or that the superposition of 

 the latter in some way favored the development of the Plutonic forces 

 which have forced molten rock for miles through narrow crevices and 

 cracks in the envelope of the globe. Perhaps the explanation may be 

 found in the supposition that the number of such dykes would depend 

 upon the number of fractures in the earth's crust, aud that this number 

 would increase with the growing weight due to thickening sediments 

 deposited by water. However this may be (and it does not explain all of 

 the facts connected with the new red sandstone), the only points where 

 have observed trap penetrating and terminating in the rocks of this belt 

 are : First, in a small exposure north of York Furnace on the Susquehanna, 

 and second, a short distance east of Black Rock post-office. 



The Belt of Azoic Schists or Phyllites (a 3 ). 



I have preferred to describe this belt under a separate heading, because 

 there are difficulties connected with its assignment, either to that part 

 of the Archaean rocks just considered, or to the Palaeozoic which will 

 next be described. These difficulties arise in great part from the lack 

 of outcrops of "rock in place." The decomposition which has at- 

 tacked this intermediate belt has destroyed the identity of the individual 

 beds and strewn the surface with its products, which are mingled with the 

 remains of rocks of much later date. This is not surprising if we may 

 assume that this belt formed the upper and later portions of the great 

 Archaean series, for we have abundant proof that in contrast to the stability 

 and repose of the broad flat arch to the south east, this new region was the 

 hinge on which the first of a number of severe plications of the strata were 

 operated. This bending and twisting unquestionably crumbled the rocks 

 and left loose material which was easily moulded by the waters of the 

 ocean, which then or subsequently covered it. to forms which more or less 

 resembled those which had originally characterized it. But after its con- 

 solidation with the next succeeding formation, and after an unknown 

 amount of erosion had laid bare their contact line, both were together simi- 

 larly treated, so that in the contorted state in which it was left it exhibits 

 some features which recall the Middle Archaean, and others wliicli remind 

 one of the Lower Palaeozoic of the county. Its precise boundaries being 

 difficult to ascertain on the ground, cannot be given with precision in the 

 text. It will suffice to say that, beginning on the Susquehanna river, a 

 short distance south of the southern outcrop of the Prospect limestone, one 

 part of it occupies all the region lying between the north-western bound- 

 ary of the Archaean already given and the southern and eastern limits of 

 the Hellam quartzite shortly to be described. It is traversed through part 

 of its extent by two large trap dykes, and contains numerous deposits of 

 iron ore which I am disposed to ascribe to segregation from iron minerals 

 in other formations. Some limestone occurs interbedded with these rocks 



