SOURCE OP ST. Peter's river. 293 



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The mineralo^ical observations were unfortunately pre- 

 rented by the circumstances under which the party tra- 

 velled. Hastening^ towards the St. Peter, and apprehen- 

 sive lest a delay on shore might deprive them of the ad- 

 vantage of a fair wind, they landed near the bluffs but sel- 

 dom, and never for any length of time. Their usual stop- 

 pages were on sandbars, and even there but for a short 

 time; they frequently travelled late at night, and some- 

 times even the whole night. Under these circumstances, 

 the only feature that could be observed, was that the coun- 

 try was formed of limestone and sandstone; that the for- 

 mer was, in one instance at least, oolitic and pulverulent; 

 that the sandstone was white, loosely aggregated, and ho- 

 rizontally stratified, but its connexion with the limestone 

 was never determined ; the sandstone prevails above Lake 

 Pepin, the limestone below it; and probably to this we 

 may attribute the difference observed in the characters of 

 the stream and its banks after we had passed the lake. The 

 sand appears to be chiefly formed by the detritus of the 

 sandstone; it not unfrequently contains cornelians, agates, 

 jaspers, &c. which present characters analogous to those 

 observed on the Rhine below Oberstein, and in ScotlancJ, 

 where they are distinguished by the name of Scotch peb- 

 bles. They bear evident marks of having been washed 

 away from a secondary trap formation. We shall have 

 occasion to observe, at a future period, that a formation 

 of this kind was traversed by the expedition. In one or 

 two instances, while examining the sand with the micro- 

 scope, a white transparent topaz was extracted from it ; it 

 is probable that had more time been taken, on land, many 

 would have been found. Although much rubbed, still the 

 form of the prism of the topaz, with its dihedral summit, 

 eould be well made out. 



