178 EXPEDITION TO THE 



which were found to consist of an amygdaloiclal rock. 

 There were a number of cavities and druses in these, 

 which were lined with minerals of the zeolite family. 

 These stones, which had been seen at the evening encamp- 

 ment near Thunder Point, had given the first intimation of 

 our approach to a formation of a different nature from 

 thoso which we had previously seen; subsequent observa- 

 tions fully confirmed the fact. On the 16th we continued 

 our voyage, but under the disadvantages arising from a 

 high and adverse wind, which prevented us from making 

 much headway; as long as we could keep under the lee of 

 the islands our progress was satisfactory, but the moment we 

 were exposed to the lake wind our boat inoved but slowly. 

 After many arduous exertions on the part of our soldiers 

 to cross one of the short channels that separate some of 

 the islands, we were obliged to retrace our course, and 

 seek a night's shelter on the last island which we had 

 passed. The geologist met here with a very interesting 

 rock, it was the amygdaloid in place. This appeared to 

 be a reddish wacke filled with geodes of quartz hyaline, 

 agate, cornelian, jasper, onyx, &c. besides mesotype and 

 stilbite. The latter mineral is found very generally disse- 

 minated ; it lines small fissures or cracks in the rock which 

 are generally not more than from one-sixteenth to one- 

 twelfth of an inch in thickness. It is of a fine red colour. 

 In the geodes we observed all those varieties of quartz, 

 which have given so much celebrity to the rocks of 

 Oberstein on the Rhine. It is impossible on beholding 

 this spot on Lake Superior, not to admit it to be a secondary 

 trap formation, similar to those of German}^, Scotland, 

 &c. We find here also, probably, the original site from 

 which have been derived all the specimens of jasper, cor- 

 nelian, &c. previously mentioned as existing on the 



