542 Geolofjical Society : — 



2. ' Notes on the Geology of Patagonia.' By John Brooke 

 Scrivenor, Esq., M.A., P.G.S. 



The author was travelling in Patagonia from September 1900 

 until March 1901. The sedimentary strata consist of Tertiary, 

 Cretaceous, and Jurassic formations, which, with the exception of 

 the Jurassic, yield interesting and varied faunas, both vertebrate 

 and invertebrate. The latest classification is that drawn up by 

 Mr. J. B. Hatcher, who conducted the expeditions sent from Princeton 

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

 has arrived at the following correlation : — 



Shiugle Formation (Tehuelche Pebble-Bed). Pleistocene. 



Cape Fairweatber Beds. Pliocene. 



Santa Cruz Beds. Upper Miocene. 



Patagonian Beds. Lower Miocene and Upper Oligocene. 



Upper Lignites. Middle Oligocene. 



Magellanian Beds. Lower Oligocene and Upper Eocene. 



Gruaranitie Beds. "^ 



Lower Lignites. 



Variegated Sandstones. i 



Upper Conglomerates. J» Cretaceous. 



Belgrauo Beds. I 



Lower Conglomerates. i 



Gio Beds. / 



Mayer Shales. Jurassic. 



Except in the north, where 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 sand- 

 stone. The Tehuelche Pebble-Bed passes down into the Cape 

 Eairweather Beds imperceptibly : otherwise it overlies everything 

 unconformably. 



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

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

 quartz-porphyr3^ 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- 



