424 Mr. Darwin on the Boulders 



Chiloe I landed on several parts of the seaward coast, but did not notice a single 

 boulder : as, however, it is separated from the Cordillera by intervening high land, 

 the absence of erratic blocks might have been expected. 



At Chiloe I again found transported boulders in vast numbers. This island is a 

 hundred miles long, extending from lat. 41° 46' to 43° 26' ; and it Ues parallel to the 

 Cordillera, at the distance of about thirty miles from their base. It consists of 

 mica-slate with two volcanic formations, largely bordered, chiefly on the eastern 

 and northern sides, with horizontally stratified beds of tertiary sandstone and vol- 

 canic grit ; the sandstone in some places passing into a loosely aggregated conglo- 

 merate. On the eastern coast the land is indistinctly modelled into successively 

 rising plains, of which the superficial parts, and the whole thickness of some of the 

 lower plains are composed of stratified shingle. This accumulation, where it caps 

 the tertiary deposits, is evidently of subsequent formation ; but I do not pretend 

 to distinguish, in all cases, the shingle beds of more recent origin, from the above- 

 mentioned tertiary conglomerate. The boulders occur in extraordinary numbers 

 on the whole line of the eastern and northern beaches, and likewise to the height 

 of at least 200 feet on the land. I saw a few imbedded in the cliffs of gravel ; and 

 as many extensive reefs show that there has been much denudation, I presume 

 that many of the masses were originally included in the gravel. The boulders are 

 likewise very numerous on the islets, which lie close to the eastern coast of Chiloe, 

 and are separated from it by channels, which, although very narrow, vary in depth 

 from 50 to more than 300 feet. In two places where I visited the outer or western 

 coast of Chiloe, I did not see any transported blocks, nor did I during a ride of 

 about thirty miles across the central high land. 



The boulders consist of several varieties of granite and syenite ; those of the latter 

 rock are common on the northern beaches ; but all the masses which I noticed 

 thirty miles southward were of granite. Their parent rock probably exists in the 

 Cordillera : an intelligent resident pointed out to me several varieties of syenite and 

 granite at the northern end of the island, which, he assured me, he had seen form- 

 ing whole mountains in the vicinity of Reloncavi Sound, which is situated in the 

 same latitude: if so, these boulders must have travelled more than forty miles. I 

 saw no granite or syenite in Chiloe, there is certainly none on the northern or on 

 the eastern coast, the whole of which I examined, and I feel pretty sure none 

 occurs in the northern part of the island ; but it is not improbable that some of 

 the western heights, which were estimated at 3000 feet, may be formed of granite. 

 If any of the boulders have come from the heights of Chiloe, they have crossed a 

 broad and level border of the tertiary deposits ; but it is far more probable that 

 all came from the Cordillera. The larger boulders were quite angular, and re- 

 sembled fragments at the foot of a steep mountain. One mass of granite at Chacao 



