Pliocene. 

 ... IJppEB, Miocene. 

 Lower Miocene and Upper Oligocene. 

 ... Middle Oligocene. 

 Lower Oligocene and Upper Eocene. 



136 Reports and Proceedings — Geological Society of London. 



Princeton University. Mr. Hatcher, aided by Dr. Stanton and 

 Dr. Ortmann, has arrived at the following correlation : — 



Shingle Formation (Tehuelche Pebble-bed) Pleistocene. 

 Cape Fairweather Beds ~ 



Santa Cruz Beds 



Patagonian Beds 



Upper Lignites 



Magellanian Beds 

 Guaranitic Beds 

 Lower Lignites 

 Variegated Sandstones 



Upper Conglomerates )- Cretaceous. 



Belgrano Beds 



Lower Conglomerates 



Gio Beds 



Mayer Shales Jurassic. 



Except in the north, vi^here intrusions of an acid type have 

 disturbed the sediments, the southerly dip is so gentle as only to 

 be appreciable where sections can be followed for some distance. 

 Mr. Hatcher considers that an unconformity separates the Magel- 

 lanian and Guaranitic Series, also the Cretaceous and Jurassic. 



Excellent sections of the Patagonian Beds were seen on the Santa 

 Cruz River and in the coast-section at Monte Leon. They are 

 littoral deposits, consisting of sandstones and mudstones. Calcareous 

 nodules are frequently arranged along the bedding-planes. Petro- 

 logically the sandstone is remarkable for containing fresh hyper- 

 sthene and plagioclase. At Monte Leon the top of the Patagonian 

 Beds is marked by gypseous mudstones and a shell-bed. These are 

 succeeded by estuarine beds, some of which yield impressions of 

 Fagus. Conformable on the estuarine beds are the famous Santa 

 Cruz Beds, which have yielded a rich vertebrate fauna. They 

 consist chiefly of pumiceous mudstones, with a little hypersthene ; 

 but a blue clay alternates with the mudstones, and there are also 

 two bands of Ostrea ingens, and one or two of ferruginous sandstone. 

 The Tehuelche Pebble-bed passes down into the Cape Fairweather 

 Beds imperceptibly ; otherwise it overlies everything unconformably. 



Very little is known of the igneous rocks. Apart from those 

 of the Cordillera, there are vast plateaux of basalt and intrusions 

 of quartz-porphyry. A good example of the' latter occurs at Port 

 St. Helena. The specimens of igneous rocks collected from the 

 moraines of the Cordillera comprise biotite-granite, hornblende- 

 granite, quartz- mica -diorite, gabbro, hornblende -picrite, quartz- 

 porphyry, rhyolite, obsidian, ophitic olivine-dolerites, olivine-basalts, 

 and acid tuffs. 



The basalt-flows cover an enormous area. They slope gently 

 towards the Atlantic, and are cut off from the Cordillera by 

 a longitudinal depression. In the neighbourhood of Lago Colhuape 

 there seems to have been a distinct centre of eruption, apart from 

 that which commences nearer the Cordillera. All that can be said 

 of their age is that they are older than the transverse depressions 

 "of the Cordillera, and older than the glaciation of the eastern slopes 

 of that chain. 



