Quartz-feldspar dikes have been found in the Hardyston sandstone of Cambrian age where it directly overlies the pre-Cambrian rocks in the Pennsylvania Highlands. The occurrence is in the east end of Morgan Hill along the Delaware River, in the eastern part of Northampton County where the roughly parallel ridges of the Highland area strike nearly east and west.
The quartz-feldspar introduced material occurs in the lower few feet of the sandstone in groups of small lenticular dikes only a few feet long and usually not more than a few inches thick. Microcline and apatite were formed first and were later invaded by an abundance of quartz which has replaced the feldspar to a large extent.
The pegmatitic invasion of Lower Paleozoic rocks has long been recognized in the Philadelphia area but the writer is not aware that it has previously been reported in the Pennsylvania Highlands.
With the finding of definite pegmatitic material of Paleozoic age, it may be reasonably assumed that much of the silicification of Paleozoic rocks of the area has been accomplished by magmatic solutions; also it is likely that at least some of the quartz veins in these rocks were formed from solutions of magmatic origin, which in their less aqueous and more siliceous phases formed pegmatites.