18 GEOLOGICAL RESEARCHES IN 



The fuel, from this place, is almost all used in the tile-glazing establishments of 

 Peking. 



Porphyries. — In the mountains north of the Wangping coal basin, the limestone 

 has been much disturbed by the intrusion of porphyry, which, in some places, 

 traverses it in the form of large dykes, and in others rising under it in large dome- 

 like masses, causes the overlying strata to dip from these in all directions. 



As the porphyry conglomerates, at the bottom of the Coal series, are mostly 

 derived from these rocks, their eruption took place before the Coal measures were 

 deposited. Two varieties of felsitic porphyry were observed here, both younger 

 than the limestone, and both represented in the conglomerate. One of these forms 

 dykes on the ridge of Hiamaling and along the Hun Ho, between this ridge and 

 Chingpaikau. At the first-named place, it incloses immense fragments of the 

 black clay slate that divides the upper and lower members of the limestone. 



This porphyry contains, in a compact, slightly greenish base, a little green mica 

 and numerous crystals of a triclinic, milky-white and slightly opalescent feldspar, 

 and is free from visible quartz. The feldspar weathers yellowish-red, and the base 

 dirty-white. The rock strikes fire with the steel, though not very readily. 



Near Yenchi, on the Hun PIo, a few miles beloW Hiamaling, is the second variety. 

 It contains, in a light-pink base, crystals of feldspar, apparently orthoclase, and no 

 visible quartz. The porphyry that cuts off" the coal rocks near the Tatsau, is proba- 

 bly younger than the Coal measures, although it is uncertain whether it occurs in 

 that locality as a dyke, or whether it is brought into the position it there occupies 

 by a great fault. 



This rock has, in a compact gray base, tending to green, numerous prisms of 

 hornblende and small crystals of white feldspar, some of which at least are triclinic. 

 It contains no visible quartz, and strikes -fire with difficulty. Thus its character- 

 istics are those of a hornblendic porphyry. 



At Chingshui, two varieties of porphyry were observed, both traversing the coal 

 rocks. In one of these, the base is black and fine-grained, containing numerous 

 minute and small crystals of a transparent, colorless feldspar, certainly for the most 

 part triclinic. There is no visible quartz, and the rock strikes fire with difficulty. 



About ten miles S. E. of the entrance to the Nankau pass, near the granite point 

 that juts out into the plain at Yangfang, there is an extensive fault in the limestone, 

 the strata of this rock dipping toward the fault. Between the line of this fault 

 and the granite there is a broad dyke of quartziferous porphyry. In a fine-grained 

 pink base, it contains crystals of pink orthoclase and abundant grains of quartz. 



It may not be out of place to mention here the coal districts of Muntakau and 

 Fangshan. The former of these forms part of the Wangping basin where this dis- 

 appears under the plain of Peking. The valley of Muntakau fornix in itself a 

 small bay, containing terraces of the plain deposit ; there are said to be thirteen 

 seams of anthracite in the sides af the vaUey, most of which have been worked 

 since during the Ming dynasty. 



Those seams which I visited alternate with sandstones and argillaceous shales, 

 and underlie the peculiar green quartzose conglomerate that characterizes the lower 

 part of the Chaitang series. 



