210 Scientific Proceedings, Royal Duhlin Society. 



called Buitreras, there are some wonderful examples of lava erosion. In a 

 general bird's-eye view of the river valley, looking westwards from the 

 southern edge of the river, we see in the distance a volcanic cone forming 

 part of the edge of the river valley. It has been cut clean in two through 

 its centre, like an apple divided through its middle by a knife. 



PI. VII, fig. 3, gives a nearer view of this cone ; it is about three hundred 

 feet high, and of the southern half nothing whatsoever remains. Across the 

 river valley, however, which is here a few hundred yards wide, the edge of a 

 lava-sheet is found, which was probably at one time continuous with this cone. 

 This means that the river valley, which has here been cut down to a depth of 

 over eighty feet, has required for its formation the removal of not only a 

 considerable lava-sheet, but also of half of a volcano cone three hundred feet 

 high. Now, if we follow down tb.e Gallegos river to its mouth some fifty 

 miles away, we find practically not a single block of lava bigger than a 

 few inches in length, and even these are few and far between. The river 

 valley is throughout covered with the usual shingle, sand, and silt. Millions 

 of tons of solid hard basalt have been removed from this area in some com- 

 paratively recent geological time, and there is no trace of them in the river 

 valley below. The terrace which has been here cut through is the lowest in 

 the Gallegos river valley, and consequently represents the erosive action, if 

 not of the latest, at least of one of the latest flood periods. The basalt here 

 is a very hard stone, and we can only wonder what has become of the millions 

 of tons which have been torn out of this place and swept away. They may 

 be buried in the floor of the river valley ; but, if so, heaps of them should 

 show above the surface in some localities. This is not the case, and we may 

 consequently conclude that these great lava blocks have either been ground 

 into fine material or carried bodily away to sea. It is difficult to imagine 

 that these huge fragments, many of them weighing many tons, could have been 

 ground up into fine shingle during the last flood period. T will here quote 

 from my note-book: "25th March, 1915. The western end of the Buitreras 

 table, although consisting of bed-rock (sheet of basalt), has its surface very 

 broken. Curious hollows, ending blindly towards the west, but often opening 

 towards the east, in the form of caliadones are found, and some small hollows 

 are found without any opening. Some of these caliadones, which are always 

 blind towards the west, are cut deeply back into the lava towards the west, 

 and have some small amount of shingle on their bottoms. Towards the 

 eastern end of the western half of this table there is extensive surface- 

 erosion of the lava ; the latter seems to have been eaten into by the caRadones 

 mentioned ; on the sides of some of these there are actual clifls of lava up to 

 twenty feet high." The Buitreras table here mentioned is an elliptical- 



