and contemporaneous Deposits of South America. 425 



was a rectangular oblong, measuring fifteen feet by eleven, and nine feet high : 

 another on the north shore of Lemuy islet was pentagonal, quite angular, and eleven 

 feet on each side ; it projected about twelve feet above the sand, with one point 

 sixteen feet high : this fragment of rock almost equals the larger blocks on the 

 Jura. There were very many others from two-thirds to a quarter of these dimen- 

 sions. The boulders amongst the islets were in fewer numbers and more rounded 

 than those on the open parts of the eastern coast ; but I believe this remark ap- 

 plies only to the smaller masses, which may have been rounded subsequently to 

 their first transportal. 



The position of the boulders at the extreme northern point of Chiloe, where a 

 headland about 250 feet high is joined to Lacuy peninsula by a quite low neck, de- 

 serves further notice. This headland, from the similarity of its composition, height 

 and stratification, must once have been continuous with the coast of Chiloe. The 

 ancient currents of the sea, which almost insulated the headland, deposited on its 

 inland side, and on the opposite coast, beds of regularly stratified shingle. Some 

 boulders were enclosed in these strata, and many very large angular ones of 

 syenite were lying both on the low sandy isthmus, and on its sides at a height 

 of 150 feet ; and transported blocks were certainly far more numerous here than 

 in any other part of the surrounding country. Anterior to the elevation, which 

 has taken place within the post-pliocene period, the headland must have been 

 an island, and the present low neck of land the bottom of a channel, open to 

 the rush of tidal waters which flowed between Chiloe and the mainland of Ame- 

 rica, We thus see, even more clearly than in Tierra del Fuego, that there is an 

 evident relationship between the distribution of the boulders, and the lines of 

 either anciently or now existing straits. From this consideration, I was at 

 first surprised at the occurrence of numerous blocks in the tortuous channels, 

 between the islets and eastern coast of Chiloe ; but I overlooked the fact, that, 

 anterior to the modern period of elevation just alluded to, the middle part of 

 Chiloe, in the line of the Lake Cucao, must, from its lowness, have been breached 

 by a transverse channel. Had the space between Chiloe and the Cordillera been 

 converted into land, the boulders, in their position with respect to their probable 

 parent rocks, in their size and angular shape, would have resembled those on the 

 Jura ; the blocks of granite now lying between the islets, being the representatives 

 of those which, M. Agassiz has lately shown, occur in the interior valleys of that 

 range. 



Of the few imbedded boulders which I saw, most were in the stratified gravel ; 

 but I find in my note-book two sections obtained in the southern half of the island, 

 and described as consisting of hardened mud, including angular as well as rounded 

 fragments of far-transported rocks, and in one instance a boulder. These deposits 



