Notice of a Scientific Expedition. 



341 



formed or has passed into a loose friable oxide of iron so tender, that 

 it may be brushed off with the least touch ; the diameter evidently 

 increases downward towards its base. Color brown* Specific grav- 

 ity =2*87. Effervesces in some places with acids. It is probably 

 composed of carbonate of lime, oxide of iron and other carbonates. 

 Narrow seams of calcarous spar traverse it in various directions. 

 There are numerous cavities running longitudinally or in the direction 

 of its fibres and which are partially intersected by transverse portions; 

 these cvaities are lined by crystals of calcareous spar. It is mineral- 

 ized, as has already been remarked by carbonate of lime and the ox- 

 ide of iron, a fact somewhat inexplicable, and unexpected, for it would 

 be more likely, we should think, to be mineralized by silex as it is 

 imbedded in rock composed principally of siliceous particles. The 

 examination of this relic has led us to imagine that it was in a decayed 

 state when the process of mineralization commenced, and that it was 

 in a state similar to the dead and decayed hemlock, so common in the 

 open fields of New England. The question most interesting in regard 

 to this fossil is, to what order of plants does it belong ? To determine 

 this, I have prepared sections of it agreeably to the method of Messrs. 

 Witham and Nicol. These sections, it is generally known, are thin 

 slices ground and polished and cemented to glass by Canada Balsam. 

 They must of course be sufficiently thin to transmit light. A trans- 

 verse section of this tree prepared as above stated, is represented 

 in Fig. 5. This section is seen by transmitted light, and is magni- 



Fig. 5. 



Fig. 6. 



fied fifty times. On comparing its structure with the fossils of which 

 Mr- Witham has given figures in his work on vegetable fossils. I 

 find that it very nearly resembles in its structure the wide, open tree, 



