• Fenton — Physiography and Glacial Geology of S. Patagonia. 203 



From the above we see that at some period during the time when the 

 river valleys were bein.c; cut out, and while the rivers were still exercising an 

 erosive action, high dry westerly winds blew over the country with great 

 violence. Volumes of gritty particles were carried along, and all rock 

 surfaces exposed were extensively eroded. In some places there are large, 

 hard basaltic fragments, which must have lost upwards of a third of their 

 bulk in this manner, and in more than one place a stone occurs which, from 

 its shape and general direction of its grain, must have had fully a ton weight 

 or more of its substance removed by wind action. On going through the 

 volcanic area, I was struck by the fact that quite a number of the cones had 

 a long slope upwards in one direction, and a steeper descent on the other 

 side; for instance, in the chain of the North Hills, out of eight hills, two had 

 this slope. I have also noticed this feature in several other places, and the 

 highest side lies always towards the east. The central craters in these sloping 

 cones are often found to a lai^ge extent filled up, and the edges of the rims 

 are as a rule rounded. I now conclude that the high wind was the cause of 

 this phenomenon also. We have already seen that we have reason to believe 

 that the great flattened condition of the pampas was produced by high winds 

 in pre-glacial times. We see now that during inter-glacial times there were 

 periods also when high winds prevailed. Before concluding, I wish to 

 state one objection. At a place on the Gallegos Eio Chico, situated about 

 thirty-five miles from its mouth, the river curves round and runs in a 

 north-westerly direction. The terrace on the left bank is here almost 

 a hundred feet above the bed of the river valley, and it is capped with 

 lava, which falls in the form of a clean cliff a short distance from the 

 top. On the summit of this cliff the usual wind-grooving runs from behind 

 right out to the edge, and it is well marked all along. When climbing this 

 cliff one morning, I was suddenly startled by seeing the typical grooves 

 running down its face almost perpendicularly. These facts are a difificulty 

 for the wind theory, as it is impossible to conceive that hard particles 

 travelling along the top with such force as to cut the stones would not, by 

 virtue of their momentum, be carried clear of the edge in their descent. I 

 will return to this subject later on, when I hope to show that far outside the 

 limits of the great moving ice-sheet there was also another form of local 

 ice-action at work. 



VT. 



Origin of the Terraces in Spring Floods of the Ice Age. 



If we take for examination any typical portion of one of the river valleys, 

 such as that of the Gallegos river, the floor of the valley is, perhaps, a mile 



