42 GEOLOGICAL RESEARCHES IN 



Although the disturbance, which was to produce the N. E. S. W. system of folds, 

 appears to have been in operation before the deposition of the limestone, it was not 

 imtil after the completion of the coal-bearing series, that this action cumulated in 

 the great revolution by which the eastern portion of the continent received its out- 

 line, and the coal-bearing strata and older rocks were folded and prepared for the 

 almost universal metamorphism that has affected them.^ 



An immense hiatus now occurs, for filling which there are no observed facts. 

 This extends over the whole time that passed between the deposition of the coal- 

 bearing rocks and the period of volcanic action in Southern Mongolia. 



During this period occurred the eruption of the Kalgan trachytic porphyry and 

 the deposition of its pluto-neptunian beds, and the outflowing on a gigantic scale, 

 along the 41st parallel, of trachydoleritic and basaltic lavas. 



The next phenomenon, of which the effects are visible, was the great dislocation 

 by which at least the southern edge of the Mongolian plateau was raised. Near 

 Fungching we have seen the high escarpment of the table-land, caused by this 

 fault, trending away in a E. N. E. W. S. W. direction. If we produce this line 

 toward the E. N. E. we shall find that it cuts the highest known point of the 

 southern edge of the plateau — that near Ha Noor. The action of springs, that 

 seem to rise along this fault line, is visible in the calcareous deposits seen near 

 Maanmiau, and on the lower plateau near Fungching. 



This great zone of volcanic action seems, as such, to mark the coast line of an 

 extensive sea or ocean lying to the north, and it is an interesting fact that it lies 

 nearly in a line with the axis of the Tienshan, in which we have every reason to 

 believe that volcanoes still exist, though perhaps only as solfataras. 



The dislocation by which the great escarpment of the plateau was formed, deter- 

 mined the depression between the table-land and the mountains south of it, which 

 was to be occupied by the lakes already mentioned. 



Before the deposition of the terrace deposit, the edge of the plateau had already 

 been subjected to extensive erosion, by which great bays and channels were cut into 

 it, and the valleys of the Te Hai and Kir Noor formed. 



We come now to an interesting question — the origin of the chain of lakes so 

 often referred to in the preceding pages, and of the deposit of loam by which they 

 have recorded their former existence.^ 



That this deposit was formed in fresh water is shown by the presence of the 

 shells found in the terrace of the Te Hai. The uniform character of the loam in 

 the different basins, and in all parts of the same basin, its great extent, and the 

 fineness of the material of which it consists, are conditions which prove that it is 

 not of local origin, or derived from the detritus of the neighboring shores, but that 

 it was brought into the lakes by one or more large rivers which must have drained 

 an area of great extent. Now throughout the region in question, the only rivers 

 are those of the Yang Ho and Sankang Ho basin, and, independently of the fact 

 that these streams drain a very small area, the valley systems of these were almost 

 entirely occupied by the lakes. 



See Chap. VII. » See Map XI, on PI. 5. 



