Fenton — Physiography and Glacial Geology of S. Patagonia. 195 



which lies with slight unconformity on the tertiary rock, and is in turn 

 overlain by the shingle ; this arrangement, howeVer, is not as simple as 

 would at first sight appear, and on careful examination one will find that 

 there is a more or less distinct transition layer between the Cape Pair- 

 weather Bed and the shingle. In a typical locality, such as is seen in 

 Cape Fairweather proper, we have first of all lying on the tertiary rock a 

 layer of fifteen feet, consisting almost exclusively of oyster shells imbedded 

 in a fine sandy matrix ; over this layer is another in which there are many 

 different varieties of sea-shells as well as oyster-shells ; the latter, in fact, are in 

 a minority ; but in addition to shells — and this is of the greatest importance — 

 there are to be found a fair number of typical pampa pebbles. This layer 

 varies from two to three up to ten or fifteen feet in thickness, and the 

 various shells, pebbles, etc., are held together by a hard rusty-brown material ; 

 in some places there is well-marked true bedding, with thin laminae of a hard 

 stone; in others there is false bedding, as if of an old beach, while in others 

 there seems to be a more or less homogeneous matrix holding the pebbles and 

 shells together. The layer in which the pebbles assume a false bedded 

 appearance, as if of an old beach, always comes between the shell-layer and 

 the shingle, and tends to fade imperceptibly into both. Now this whole bed 

 would give one the impression of being a shallow-water formation, and the 

 fact that most of the shells are practically complete, with often both valves 

 of the lamellibranchs in position, would show that it has suffered very little 

 disturbance since it was laid down, and would indicate, at the time of its 

 formation, calm shallow water. 



These facts are very significant, and tend to show that the transition from 

 r,he pre-shingle to the shingle periods was gradual; in fact, when the first 

 shingle began to be washed down from the mountains over the plains to the 

 Atlantic coast the climatic conditions were such that these marine molluscs 

 flourished in abundance ; also it is clear that calm weather prevailed, and that 

 the floods which carried down the shingle were very mild, and had very little 

 tearing up or grinding action, otherwise the shells mixed with the pebbles 

 would have been all smashed up and ground to powder. 



Later on the shingle came down in greater quantities and with greater 

 force, so that in the end the shell-layer became completely covered, and 

 nothing but pure pebbles and sand remained on the surface. These facts also 

 show that at the beginning of the shingle period the level of the main pampa 

 was much lower than at present, and that Cape Fairweather, which is now 

 almost five hundred feet high, was then slightly below or at the sea-level. 



