18091842] VOYAGE 



(few inches to feet thick) of a brecciatetl pitchstone. I Letter 6 

 strongly suspect the underlying granite has altered such beds 

 into this pitchstone. The silicified wood (particularly charac- 

 teristic) was yet absent. The conviction that I was on the 

 Tertiary strata was so strong by this time in my mind, that on 

 the third day in the midst of lavas and [? masses] of granite 

 I began my apparently forlorn hunt. How do you think I 

 succeeded? In an escarpement of compact greenish sand- 

 stone, I found a small wood of petrified trees in a vertical 

 position, or rather the strata were inclined about 20-30 to 

 one point and the trees 70 to the opposite one. That is, they 

 were before the tilt truly vertical. The sandstone consists 

 of many layers, and is marked by the concentric lines of 

 the bark (I have specimens) ; 1 1 are perfectly silicified and 

 resemble the dicotyledonous wood which I have found at 

 Chiloe and Concepcion ; 1 the others (30-40) I only know to be 

 trees from the analogy of form and position ; they consist of 

 snow-white columns (like Lot's wife) of coarsely crystalline 

 carb. of lime. The largest shaft is 7 feet. They are all close 

 together, within 100 yds., and about the same level: nowhere 

 else could I find any. It cannot be doubted that the layers of 

 fine sandstone have quietly been deposited between a clump of 

 trees which were fixed by their roots. The sandstone rests on 

 lava, is covered by a great bed apparently about 1,000 ft. thick 

 of black augitic lava, and over this there are at least 5 grand 

 alternations of such rocks and aqueous sedimentary deposits, 

 amounting in thickness to several thousand feet. I am quite 

 afraid of the only conclusion which I can draw from this 

 fact, namely that there must have been a depression in the 

 surface of the land to that amount. But neglecting this 

 consideration, it was a most satisfactory support of my pre- 

 sumption of the Tertiary (I mean by Tertiary, that the shells 

 of the period were closely allied, or some identical, to those 

 which now live, as in the lower beds of Patagonia) age of this 

 eastern chain. A great part of the proof must remain upon 

 my ipse dixit of a mineralogical resemblance with those beds 

 whose age is known, and the character of which resemblance 



GeoL Obs., p. 202. Specimens of the silicified wood were examined 

 by Robert Brown, and determined by him as coniferous, " partaking of 

 the characters of the Araucarian tribe, with some curious points of 

 affinity with the yew.'' 



