J. B. Hatcher — Geology of Southern Patagonia. 351 



well defined columnar structure ; while toward the top they 

 are usually composed of great masses of vesicular slags and 

 cinders with bright colors, jet black, steel blue, crimson and 

 yellow predominating. One of these is shown in fig. 9. The 

 columnar structure may be seen on the left near the base, while 

 toward the summit only cinders and slags prevail. The two 

 small " windows" on the left have suggested the name Sierra 

 Yentana. It is on the right bank of the Rio Chico about 75 

 miles above the mouth of the Rio Chalia and rises to a height 

 of perhaps 1200 feet. 



Eig. 9. Sierra Ventana, Rio Chico, Patagonia, from a photo, by the author. 



The Transverse Valleys of Patagonia. 



Dr. Florentino Ameghino, in his u Notes on the Geology 

 and Paleontology of Argentina," after discussing at some 

 length the bowlder formation, takes up the origin of the trans- 

 verse valleys of Patagonia. Since it appears to me that Dr. 

 Ameghino is entirely wrong here, not only in his conclusions 

 but also in his statement of facts, I quote him fully on this 

 question. He says, on page 18 : " Having now dispelled the 

 ignorance as to the origin of the bowlder formation, this leads 

 us naturally to determine the age of the formation of the trans- 

 verse valleys of Patagonia. It is evident that at the bottom 

 of the ancient sea in which the bowlders were deposited, these 

 were scattered by the waters in a uniform manner over all the 

 submerged territory. The same may be said of the sheets of 



