I24 RESEARCH IN CHINA. 
OBSERVED SECTIONS. 
Distribution.—The district within which the Hu-t’o strata occur in 
characteristic development lies southwest of the great Wu-t’ai-shan range 
and is the locus of a peculiar depression, which is to a great extent filled 
with the Huang-t’u or loess. Hills consisting of Pre-Cambrian argillite and 
limestone rise in isolated groups and ranges from the loess-filled basins. 
Similar rocks form the southwestern end of the Wu-t’ai-shan, and also 
occur in the base of the Ki-chéu-shan and its extension eastward. 
Occurrences near Shi-tsui.—Rocks near Shi-tsui belong altogether to 
the older Wu-t’ai system, and the Hu-t’o strata did not occur in any of the 
sections which we observed along the T’ai-shan-ho and its tributaries. Four 
miles, 6.5 kilometers, southwest of the village there is, however, a conspic- 
uous peak, which was occupied by Sargent as a triangulation station, and 
from which he brought back a characteristic specimen of limestone of the 
Hu-t’o system. We regard this as the most northeastern occurrence of 
these rocks at the end of the great synclinorium which stretches thence 
southwestward. 

fo) ' 2MILES 

Fic. 21 (Blackwelder. Atlas sheet C I, section A A).—Liu-yiian, Shan-si. Tou-ts’un slates and lime- 
stones (Upper Algonkian), exposed in the ridge east of Liu-yiian. a= porphyry dike; b = gray phyl- 
lites with thin reddish dolomite; c= greenstone dike; d = limestone breccia; e = gray slate; f = pure 
gray limestone; g = gray slate and reddish dolomite; h = gray slates; 7 = white quartzite; 7 = gray 
slate with gray and reddish dolomite; k = gray quartzite with conglomerate. 
East of Liu-yiian.—The mountains east of Liu-yiian and south of 
Nan-t’ai-shan are composed almost entirely of the Hu-t’o rocks (Fig. 21). 
In the first ridge we found a series of earthy gray phyllites, the Téu-ts’un 
slates, evidently derived from calcareous shales and in the early steps of 
metamorphism. The cleavage planes of these slates are frequently dotted 
with small crystals, which appear to be pseudomorphs of hematite after 
magnetite. Thin layers of red crystalline dolomite are intercalated with 
the slates at frequent intervals, and furnish a very convenient means of 
distinguishing the true bedding planes from the prevailing slaty cleavages 
Two and a half miles, 4 kilometers, southeast of this village the gray slates 
are overthrust from the west upon a syncline, which contains strata of an 
altogether different nature; white quartzite and limestone, with layers 
of gray phyllite interbedded, lie conformably upon gray and red quartzite, 
which contains local layers of conglomerate. What lies beneath the quartz- 
