4 GEOLOGICAL MEMOIRS. 



formerly flowed in the Hungarian rivers at a level of from 10 to 

 30 feet higher than it does now, viz., when their floods were able 

 to rise to the height of the old inundational areas and to occupy the 

 ancient river-beds. 



Again, the beds of the rivers must have been from 30 to 70 feet 

 higher than they are now, when land now lying at that height above 

 the present level of the Danube was covered with its water, and in 

 which, for instance, the alluvium of Csernavoda was deposited. 



Also the land must have been raised from 100 to 130 feet since 

 the deposition of the old alluvial deposits at Zimony (Semlin), Gomba, 

 Kis-Terenne, &c. 



And, lastly, there has been an upheaval of the district under 

 consideration to the extent of from 130 to 200 feet since the terrace- 

 system was formed ; these terraces, however, are not the result of 

 the action of rivers, but of that of a vast expanse of water, which 

 covered the whole area of the diluvial deposits. 



Pleistocene Period. — Towards the margin of the Hungarian basin 

 the Pleistocene (diluvial) deposits consist of gravel overlain by sand. 

 In the central portion of the great basin bordering the course of the 

 Theiss, the lower beds are formed of a bluish mud and sand, but the 

 upper portion consists of Loess. Frequently, however, the latter 

 lays immediately upon the older formations. Besides this, a calcareous 

 tufa occurs under interesting circumstances, though not over any 

 considerable area. The average thickness of the diluvial deposits 

 may be estimated at 200 feet ; they are overlain by alluvium, and 

 repose upon the highest pliocene deposit, and especially the Congeria- 

 beds. 



The gravel is characterized by boulders of trachyte, basalt, and 

 the opaline minerals pertaining to the rhyolite-group. By the 

 decomposition of some felspathic minerals the natural soda of 

 Hungary and a calcareous tufa are formed, either immediately upon 

 the surface or under a thin cover of soil. At a very typical spot, 

 between Szeged and Dorozsma, where a great quantity of soda is 

 obtained, and at a depth of 3 to 4 feet in the Soda-lake, the author 

 found grains of the size of a pea, and all of the same external ap- 

 pearance. The analysis proved them to be labradorite; and, in 

 ascending towards the surface of the lake-bed, they are found to be 

 more and more decomposed. The origin of this volcanic ejection 

 must be attributed to a volcano which was discovered by the author 

 some years ago in the basin of the Theiss, north of the Matra 

 Mountains, near Ajnacsko. 



The Loess occurs not only in Hungary, covering the greatest part 

 of the central plains and the adjacent valleys, but it is also found 

 greatly developed in the Danubian Principalities, and on the shores 

 of the Black Sea, as far as Odessa ; further the author has not carried 

 on his investigations, but there is every reason to believe that it 

 covers a great part of the northern Pontic plain. Southward from the 

 mouth of the Danube it forms the upper stratum towards the Balkan 

 Mountains. In some localities, cliffs of from 80 to 100 feet appear 

 quite homogeneous, but in most instances distinct lines of stratifi- 



