igoo-i.] Physical Geology of Central Ontario. 159 



which in some cases carry fossils that are supposed to mark a transition 

 vertically from the Chazy at least, but which equally well may mark a 

 transition horizontally. Chiefly as outliers, but occasionally passing 

 beneath the non-fossiliferous beds below the identified beds of the Black 

 River formation, are a series of sandstones usually termed Potsdam. 

 (The maximum thickness is, locally, sixty feet). As no fossils, except 

 some very obscure Scolithus borings, have, so far as the writer knows, 

 ever been found in these beds ; and as Potsdam is a term introduced to 

 describe rocks where certain definite stratigraphic and faunal relations 

 hold, it is inadvisable to apply the term until these well defined relations 

 are proven to exist here. Even were fossils found in the sandstone, the 

 possibility of their being, in this locality, contemporaneous with the 

 lower limestone beds, would not be diminished. 



Much of the sandstone of these deposits, in this area, occurs in 

 depressions between pre-sedimentary ridges. There are many angular 

 fragments of gneiss and quartz, both large and small, included in 

 the sandstone. In many places there are no known beach-worn 

 pebbles, and no fossils, even in very thick beds ; the material has 

 been well sorted and consists almost wholly of quartz grains ; the 

 beds are frequently very massive and obscurely cross-bedded ; ripple 

 marks are absent or very obscure in many localities. There thus seems 

 to be good reason for thinking that much of this sandstone may be 

 waste which was laid down here, possibly by streams, after the crystal- 

 line surface had been smoothened and freed from its residual soil, if 

 such ever existed, but before the advent of the sea, and that the shore- 

 line of that time is now concealed by the overlying deposits. Subse- 

 quently, in the rapid depression of the land immediately preceding the 

 time when the limestones overlapped upon the crystalline area, the 

 surface of these sands may have been evened off, and perhaps a small 

 amount of new material was added. 



Arkose. — There is one known locality in which the non-fossiliferous 

 sediments beneath the identified Black River limestone are especially 

 interesting. At the foot of the escarpment on Deer bay, just at water 

 level, a few well marked beds of arkose are exposed. The beds average 

 about ten inches each, the whole deposit being an unknown amount 

 over six feet in thickness. This arkose consists of translucent partly 

 worn crystals and fragments of quartz and angular fragments of pink 

 orthoclase feldspar, cemented with a dark reddish-purple feldspathic 

 and calcareous cement, with occasional patches which resemble the 

 argillaceous portions of some of the succeeding beds. The rock is 



