GEOLOGICAL RESEARCHES IN 



CHAPTEE II. 



GEOLOGICAL OBSERVATIONS IN THE BASIN OP THE 

 YANGTSEKIANG. 



A GLANCE at the section (PI. 1) across Central China will show that the Devo- 

 nian limestone and Chinese Coal measures seem to predominate, at least at the sur- 

 face, over all else. There is only one point in the whole length of the section, 

 where ropks older than the great limestone deposit rise to the surface, so that if the 

 former exist, they are buried deep below the level of the sea. I shall give, in a 

 subsequent chapter, reasons for believing that, at least in the valley of the Yangtse, 

 there are also no representatives of the Mesozoic formations of later date than the 

 Chinese Coal measures, and few, if any, of the Cenozoic. 



Where the Yangtse breaks through the ridges of the central .anticlinal axis of 

 elevation, in Eastern Sz'chuen and Western Hupeh, a section, nearly eighty miles 

 long, is exposed in the succession of deep gorges through which the river passes 

 this barrier. Here the Devonian limestone is seen to rest almost immediately on 

 the granite, a comparatively small develo]Dment of metamorphic schists intervening. 



This seems to be the only point between Western Sz'chuen and the Pacific, where 

 the Yangtse has exposed these lower rocks, and even here they occur during only 

 about eight miles of the river's course, and with a maximum height of only a few 

 hundred feet above the river. To their occurrence are due the rapids that render 

 the navigation of this part of the " Great River" so dangerous. 



The granite immediately above the first rapids consists -of a triclinic feldspar and 

 orthoclase, the former predominating, a brilliant black mica and quartz with small 

 crystals of sphene scattered through the mass. Above Shantowpien the granite 

 becomes very fine-grained, and still further up the river it is succeeded by syenitic 

 granite, composed of white triclinic feldspar, quartz, large laminee of brown mica, 

 and crystals of hornblende, with minute octahedrons of magnetic iron. 



On its eastern and western declivities the granite supports the metamorphic strata. 

 Those to the eastward, which could not be closely examined, seemed to be gneiss 

 trending E. W. and dipping about 30° to S. West of the granite the strata con- 

 sist, where examined, of hornblendic schist and chloritic schist, the former often 

 containing lenticular masses and cross veins of quartz, feldspar, and chlorite. Rolled 

 fragments of diorite, probably of metamorphic origin, indicate the presence of this 

 usual companion of these rocks. Near their contact with the granite these strata 

 trend N. N. E., dipping about 85° to E. S. E., while further up the river their trend 

 changes to E. N. E., and tlie dip to N. N. W. 



