202 Scientific Proceedinijs, Ro/jal Dublin Society. 



town, and have travelled many leagues over these rocks. In every place T 

 have studied this grooving, and, as I have said, I have never failed to find it 

 in any locality where there is lava, except in the case of the Cerro Diablo. 



V. 



Indications of Strong Westerly Winds. 



I have had many explanations offered to me as possible causes of the 

 grooving of the stones mentioned in the last section of this paper. The 

 only one, however, which is worthy of note is the action of high westerly 

 winds carrying sand, grit, &c. 



One of the most characteristic climatic features at present in Patagonia, 

 particularly during the summer months, is the strong dry winds which blow 

 from the west. These winds blow as a rule about one to two days each 

 week during the summer and autumn. As I have already mentioned, a 

 large amount of sand and dust is carried along, and I have noticed surfaces 

 of dried mud in a valley cut in grooves in the same manner as the stones 

 after a few months of windy weather. 



It is noteworthy that the grooves always run up the westerly faces of 

 the stones in aia oblique manner towards the east, as would result from 

 westerly winds blowing in dry weather and carrying gritty particles. The 

 fact also that grooves are found down in narrow spaces between stones is 

 strongly in favour of wind action. If, however, we examine recent lava- 

 sheets, such as those from the Cerro Diablo, or if we examine the large 

 blocks which have fallen down from the most recent lava cliffs bounding the 

 present beds of the river valleys, we may search iir vain for grooving. I 

 have found abundance of grooving on all the higher levels, but on the lowest 

 and last levels of the river valleys, although I have searched extensively, I 

 have never seen it in its typical and characteristic form. Another point of 

 considerable importance is that in hundreds of localities where this grooving 

 is found a peculiar rusty patination of the surface occurs, in marked contrast 

 with the clean black stone revealed when the grooved surface is chipped off 

 with a hammer. The grooved surface is now becoming weathered off the 

 stones and not weathered on. In many localities the grooved surfaces have 

 been overgrown with lichens, mosses, and other vegetable matter ; and they 

 are often hidden away behind bushes and shrubs, which are growing with 

 ease in front. The evidence, consequently, seems to point to the fact that 

 this grooved condition of the stones was brought about during some former 

 geological period, and was not produced since the river beds were cut down 

 to their present levels. 



