388 RESEARCH IN CHINA. 
wear of exposed rocks rarely possess these characteristics,* though it is 
not doubted that such conglomerates may originate by the erosion of older 
limestones under appropriate conditions of exposure.f 
The facts relating to the limestone conglomerates from Shan-tung 
seem to be best explained by some modification of the hypothesis suggested 
by Walcottt with reference to the American occurrences, viz, that the floor 
of the shallow Cambrian sea was locally raised above sea-level and eroded, 
the material being deposited in the areas which remained submerged. 
If there was actual emergence we should expect to find corresponding local 
unconformities, but in China none were observed. ‘The following hypoth- 
esis, contributed by Willis, does not postulate uplift, and therefore requires 
no unconformities: 
In true intraformational conglomerates, whether from China or the United States, the 
pebbles, although they are the peculiar part of the stratum, are nevertheless essentially 
of the same material and apparently of nearly the same episode of deposition as the matrix. 
Their constitution is commonly that of an earthy limestone; the matrix may be a similar 
limestone or limy shale. The pebbles are not derived from notably older strata, so far 
as one may judge from their constitution and contained fossils, nor do conditions exist 
which make it probable that they could have been derived from such a source by any 
recognized method of erosion. They have, nevertheless, usually been transported, more 
or less broken or worn, and redeposited. Their appearance, relations to matrix, and occur- 
rence strongly indicate that the pebbles were originally discrete solid aggregates, not 
notably different in size or form from what they are in their place of final deposition. 
A solution of the problem of the formation of these conglomerates seems, therefore, to 
be probable along the line of processes, which may result in local induration of calcareous 
mud, independently of the solidification of the mass. The effect is one of concrescence, 
but the product lacks the common aspects of concretions, especially visible concentric 
structure. 
The processes which may be suggested are chemical, physical, or organic. One 
essential condition of any such process is that the sediment shall not be homogeneous in the 
sense of being a mass of uniform chemical and physical constitution throughout. Sedi- 
ment gathering beneath currents and eddies, on a bottom inhabited by various organisms, 
probably would not be homogeneous in that sense, but to what extent and in what manner 
it would be heterogeneous is a matter of local conditions which we can only conjecture: 
With reference to induration through local concentration of carbonate of lime, it 
is no uncommon occurrence that a bed of indurated limestone lies between two beds of 
not indurated clay. Ina less extreme case, let it be assumed that in the unconsolidated 
sediment lime-carbonate is passing into solution through reaction with organic matter, 
and diffuses itself through a certain mass. Suppose that mass to be a small thin lens 

* Campbell has described, from the Cambro-Ordovician limestone of Virginia, a limestone conglom- 
erate which rests upon an eroded surface within the formation. Here the evidence of erosion, whether 
terrestrial or subaqueous, seems clear. (Campbell, M. R., G. S. A. Bull., v, p. 175.) 
{ Pure limestone conglomerate is now forming locally in Lake Temiscaming, Ontario, through the 
wear of the waves upon cliffs of Silurian limestone and the lodgment of the gravel in a calcareous mud, 
(W. O. Hotchkiss, unpublished notes, 1905.) 
t Loc. ctt., pp. 197-198. 
