STRUCTURAL GEOLOGY OF SHAN-TUNG. 61 
STRUCTURE OF THE SINIAN SYSTEM. 
GENERAL CONSIDERATIONS. 
Original lay of the strata.—At the base of the Sinian system is a plane 
of unconformity, which is extensively exposed in the Ch’ang-hia and 
Sin-t’ai districts, and is a flat, even surface. The slight irregularities of 
the basement, which project up into the lowest Sinian sediments, are 
insignificant as compared with the thickness of superincumbent strata; and 
it is only when considered over extensive areas that the surface departs 
notably from a flat. In so far as it does so, it conforms to the folds in the 
Sinian system, and the flexures are clearly effects of deformation and 
not original. It is therefore a reasonable inference that the surface upon 
which the Sinian strata were first laid down was one which had been reduced 
by erosion and marine planation to a condition of flatness and evenness. 
The lowest beds of the Sinian system are shales and sandstones, in general 
about 500 feet, 150 meters, thick. They filled in the slight inequalities in 
the surface of the Pre-Cambrian rocks, and when the conditions of sedi- 
mentation became favorable to the deposition of limestone, these clastic 
sediments had the nearly flat surface of a gently sloping sea-bottom. 
Measurements of the limestone strata are in general uniform; only in 
the Ch’ang-hia oolite do we find considerable variations, and there the 
differences in thickness of the limestone masses appear to be compensated 
by accumulations of shale. The overlying Ch’au-mi-tién limestone is very 
uniform in character and thickness, and the same is true of the great 
Tsi-nan-fu limestone, so far as it is preserved. If these observations be 
correct, the Sinian system, within the province of Shan-tung, originally 
presented an extensive and essentially flat mass of strata; initial dips 
were very local and slight, and there were no long lines of initial flexure, 
which, in later deformation, might have given rise to prominent and 
extensive anticlines and synclines. We would therefore expect that defor- 
mation of the Sinian system by compression would result in local folds 
within the system, and that where larger flexures had developed they 
would be of a very broad and gentle character. This inference accords 
with the observed facts. 
Relative rigidities of the Sinian formation.—The Sinian system, con- 
sidered as a whole, is a rigid mass, capable of transmitting thrust through- 
out a large area; but the individual formations differ greatly in rigidity. 
The Man-t’o formation, at the base of the system, is composed of 
500 feet, 150 meters, of thinly interbedded shale and limestone, with 
occasional thin beds of sandstone. The layers are discontinuous, except 
the limestones, which, though persistent, are too thin to affect the com- 
