162 D. DALE CONDIT 
abundantly provided with garnet. Glacial drift drawn from such 
sources has so much of the mineral that it is second only to quartz 
in abundance. The Triassic beds of the east, fairly reeking with 
garnet, furnish an illustration of a sandstone built largely from 
materials derived rather directly from the crystallines. Condi- 
tions of sedimentation during ‘‘Coal Measures,’? Mauch Chunk, 
and Catskill time were probably not greatly different from those 
that prevailed during the formation of the Triassic beds. All are 
either continental or near shore in origin. 
To the writer it seems that the difference in mineral content 
between the Triassic and the older sandstones indicates a quite 
different source of material. While it is obvious that gneisses and 
schists contributed very extensively to the Triassic beds, it seems 
probable that such rocks did not furnish much of the materials 
of the older sandstones. A large portion of these have doubtless 
come from crystalline sources, but the minerals indicate that the 
rock may have been igneous rather than metamorphic. It is 
conceivable that a peridotite or gabbro furnished the ferromagne- 
sian minerals so abundant in the Catskill series, while a granite 
was the source of the zircon, tourmaline, and muscovite of the 
‘‘Coal Measures”’ sandstones. 
It is becoming more and more evident to geologists that the 
mountain-making processes which took place at the close of the 
Paleozoic were accompanied by the intrusion of extensive igneous 
masses and the metamorphism of the country rock into schists. 
The work of Loughlin’ and others has demonstrated the magnitude 
of these changes in Rhode Island. A number of intrusive masses, 
mostly granite, in the bighland region of New York and New 
Jersey, are known to be post-Ordovician and may be of the same age 
as those in Rhode Island. Recently a report has come from Vir- 
ginia of the finding of fossils in schistose slates of the Piedmont 
belt. These slates were formerly regarded as pre-Cambrian but 
the fossils show them to be Upper Ordovician in age.*. Thus it is 
1G. F. Loughlin, “Intrusive Granites and Associated Metamorphic Sediments 
in Southwestern Rhode Island,’ Am. Jour. Sci., XXIX (1910), 447-57. 
Thomas L. Watson and S. L. Powell, ‘Fossil Evidence of the Age of the Vir- 
ginia Piedmont Slates,’ Am. Jour. Sci., XX XI (1911), 33-44. 
