1862.] AUSTIN SIBERIA. 71 



the Rio Plata. This lower mass contained no fossils, and its age 

 is of course unknown* ; but, I may add, that I saw at two points in 

 Western Banda Oriental, beneath the marine tertiary strata, beds 

 of red clay with marly concretions, which, from their mineralogical 

 resemblance to the overlying Pampean formation, seemed to indicate 

 that at an ancient period the Eio Plata had deposited an estuarine 

 formation, subsequently covered by the marine tertiary beds, and 

 these by the more modern estuarine formation, with its remains of 

 numerous gigantic mammalia ; and that, finally, the whole had 

 been elevated into the present plains of the Pampas. 



4. Geological Notes on the Locality in Siberia where Fossil Fish 

 and Esthers have been found. By C. E. Austin, Esq., Mem. 

 I.C.E., F.G.S. With a Note on Estheria Middendorfii ; by 

 Professor T. Rupert Jones, F.G.S. 



(Abridged.) 



In 1858 I had the pleasure of presenting to the Society some slabs 

 of fossiliferous shale, containing specimens of the fossil fish men- 

 tioned by Dr. von Middendorf f as having been obtained by him at 

 Nertchinsk, during his last journey in Siberia, and named Lycoptera 

 Middendorfii by J. Midler J. 



The slabs also contain the remains of a number of Estherice, 

 referred to by Miiller as Limnadiai§, as well as portions of reeds and 

 stems of plants, some lignite, and two imperfectly preserved shells 

 which probably belong to a species of Limnwus, but may possibly be 

 Paludince. They were taken by me from the bed, in situ, in the year 

 1848. 



The bed lies about 160 versts south by east of Nertchinsk, at the 

 base of a cliff from 6 to 10 feet high, extending north and south, and 

 forming the west or right bank of a small clear stream, called the 

 Toorga, which flows southward into the River Onon. The bed dips 

 westward about 25°. 



The east bank of this stream, where it flows by the fossiliferous 

 strata, rises gradually, and extends, above the level of the water, 

 into a plain, on which conspicuous masses of igneous rocks are dis- 

 tributed. 



At a point eight versts to the south of that where the fossils were 

 found, an abrupt hill of augite -porphyry rises from the plain to an 

 elevation of more than 100 feet. Its southern face is composed of 

 rhomboids cemented together by quartz into one solid mass, and 

 thus a rock is formed which is not uncommon in the mountainous 

 districts of Siberia. 



* It was supposed by Dr. Burmeister to be Silurian. 



t A. Th. von Middendorf s ' Siberische Reise,' Band i. Theil. 1. Einleitung ; 

 Klimatologie ; Geognosie. Fossile Fische, bearbeitet von Johnnes Miiller: 4to. 

 St. Petersburg, 1847. See also Quart. Journ. Geol. Soc. vol. vi. part ii. Miscell. 

 pp. 45-48. 



J Op. cit. p. 262, pi. 11. § Op. cit. p. 261. 



