TIERRA DEL FUEGO. 603 
aspect when broken. Occasionally it is difficult to distinguish the 
included pebbles on a fractured surface, on account of their earthy 
appearance and resemblance to the intervening material: the true 
structure in these instances is apparent on a worn surface. In gene- 
ral, however, the conglomerate character is obvious. The pebbles 
are of various colours, the most common of which are brownish-black, 
brownish-red, greenish and red; and in some places they are a foot or 
more in diameter. On Burnt Island, which forms the southern side 
of Orange Harbour, the coarse conglomerate contains large masses of 
porphyritic trap, one of which was three feet in diameter. Although 
pebbles of trap, porphyry and trachyte are abundant in these beds, I 
found none of granitic rocks. 
These coarse conglomerates pass gradually into sandstones; and 
some layers of the latter so closely resemble the greenstone of the 
region, especially when broken, that they could scarcely be recognised 
except by observing their transitions. 
Lines of deposition are not distinguishable in the coarse conglome- 
rate beds: they form layers fifteen to twenty feet thick, alternating 
with the other varieties of the formation without horizontal or vertical 
lines of separation. 
The beds on Burnt Island present the same characters as on the 
coast. Coarse conglomerates constitute the lowermost layers; and upon 
these rests a fine breccia having a calcareous cement. Next follows 
a similar conglomerate without lime, the fracture of which is remark- 
ably earthy, and the colour dark and nearly uniform. Next above is 
a fine variety of the same rock, resembling a sandstone in texture, but 
apparently argillaceous in composition. ‘The succeeding layer ap- 
proximates more to an argillaceous shale of fine texture. 
Dip and Strike of Beds —The rocks in the region examined are 
seldom horizontal, but dip generally from twelve to fifteen degrees to 
the westward. Passing along the coast from the head of the Bay, I 
found the dip as follows in different places :— 
West-southwest half south, fifteen degrees, 
West by north, eleven degrees, 
West by north, twenty degrees. 
West by north, thirty-five degrees. 
Northwest, nearly vertical. 
Northwest, nearly vertical. 
These directions and the amount of dip are dependent, in part, on the 
intersecting dikes. At one place on Burnt Island, the layers resting 
