404 R. D. Irving—St. Peters and Potsdam Sandstones. 
above alluded to. Beginning first with the Baraboo quartzites. 
I noticed at once in many sections, as viewed in ordinary 
light, a distinct clastic structure, rounded grains of quartz, out- 
lined often by a little film of iron oxide, making up most of the 
section, but with a clear quartz in the interstices. Often some 
of the quartz grains would seem ill-defined, and look as though 
they melted away into the interstitial quartz; an appearance 
which has been noted by other observers in sections of the 
quartz-rocks of various regions. In polarized light, however, 
it was often observed that all appearance of a clastic nature 
or to restore a broken crystal, after the lapse of many ages, 
was to me a new conception, and one which seemed to call for 
very rigid demonstration before acceptance. There was little 
difficulty in proving that the apparently fragmental quartzes 
