Analysis of Tin Pyrites. 33 
near the junction of the lower sandstone with the calciferous, 
there are several alternations of calcareous and silicious bands, 
the latter having the character of the sandstones below, and the 
former of the calcareous deposits above. These occur in several 
places on the upper Mississippi river, and give the geologist an 
introduction to that condition of things which subsequently pro- 
duced the upper sandstone, which is distributed over a large part 
of Wisconsin, so often mistaken for the lower member of the 
series ; but which, in fact, is separated from it by two or three 
hundred feet of calcareous rocks. 
This upper sandstone can be regarded in no other light than as 
the result of the same causes which produced the Potsdam, and 
pected. It is, nevertheless, shown in many places within the 
Lake Superior district, that the true sandstone, as it is traced 
upward, becomes gradually calcareous, and “ finally passes into 
well-characterized, compact, magnesian limestone.”* The same 
1s true, also, of this rock, in Canada and New York; while, how- 
ever, there is rarely any evidence of increase in the silicious 
materials towards the termination, as we.observe in the west. 
In some localities, there are thin but distinct bands, near the 
Upper portion, having an oolitic structure, which, as we go west- 
ward, appear to be replaced by beds of a granular texture and of 
a silicious character. 
Arr. Ill.—Analysis of Tin Pyrites ; by Dr. J. W. Mauvet.t 
_ Tuts rather rare mineral is one of which the chemical compo- 
sition has appeared somewhat doubtful, owing to the considerable 
discrepancy between the three or four analyses which have been 
* Part 1, p. 117. + Communicated for this Journal. 
SReonp Serres, Vol. XVII, No. 49.—Jan. 1854. 5. 
