April 20, 1877.] ^^1 [Frazer. 



Regarding some Mesozoic Ores. 

 By Persifor Frazer, Jr. 



{Bead before the American Philosophical Society, April 20, 1877.) 



There are several places in the New Red Sandstone where, although 

 the presence of no other formation within several miles is intimated on 

 the old map, nor has any sudden change of character in the rock been sus- 

 pected, there nevertheless appear to be good reasons for supposing that 

 the outer shell of the Mesozoic strata has been worn through and the un- 

 derljdng and older formation has been exposed. One instance (of not 

 much w^eight, owing to its very local character and its proximity to the ac- 

 tual boundary between the two formations) occurs near Franklintown, 

 York County, near Lerew's tavern, where an oval piece of ground seems 

 to be composed entirely of the older schists, while the contiguous country 

 is made up of the newer shales and sandstones. 



The same thing may be noticed near Bendersville and near Arendtsville, 

 where small islands of Mesozoic seem to stand out in a sea of Huronian schists 

 and debris. Many such instances taken from other formations will occur to 

 every geologist, and a glance at the State geological map of the last survey 

 will convey the same fact forcibly through the eye to the mind ; for 

 there it will be seen that not only are the bounding edges of the formations 

 ragged, and the shreds of one left within the domains of tl e other, but 

 (sometimes on account of the geographical and orographical conditions under 

 which the original deposition of beds took place ; and sometimes owing to 

 the peculiar action of erosion) great peninsulas, islands and archipelagos, 

 are to be seen distinguishing themselves from the formation in which they 

 lie by the colors chosen by Prof. Rogers to represent them. 



Such, for instance, are the strips of what Prof. Rogers called Primal and 

 altered Primal which stretch out like an Aleutian chain in the limestone 

 sea of Lancaster and York Counties. 



So far as this occurrence of the Huronian rocks within the limits of the 

 New Red Sandstone is concerned, it is important in more ways than one. 



Ist. As accounting for the presence in the newer of many constituents 

 characteristic of the older rocks in other parts of the country (magnetite, 

 copper ore, etc.) ; and 2d, in resolving the doubt as to the comparative 

 thickness of the New Red Sandstones at adjacent points. 



It has long ago been suggested that the presence of the iron " Glances" 

 in the red shales and sandstones, and the presence in the latter of more or 

 less well defined belts of copper ore, might be accounted for on the suppo- 

 sition that in the making of the newer beds the older were ground up and 

 redistributed {re-sediment ed would better express the idea). 



We know as a fact, adverted to elsewhere, that the only horizons in which 

 copper ores have been found in this State are the South Mountain series of 

 crystalline schists, etc., and these very rocks in question. And even if we 

 seek elsewhere in this country, except a very limited deposit in the Medina 



