H. C. Sargent—Carboniferous Cherts in Derbyshire. 265 
adjoining area of Chi-li and Shan-si and in the Tai-shan districts, 
western Shan-tung, the Tai-shan Complex. Further, they distinguish 
in the Tai-shan Complex at least three groups of rocks: the oldest 
consists of a chaotic mass of hornblende-schist, mica-schist, chlorite- 
schist, and other highly altered rock material that may have been 
derived from true aqueous deposits. In the Complex are found large 
intrusive bosses of acid composition, accompanied by offshoots of 
pegmatite, aplite, quartz-veins, etc. These are in general highly 
altered or strained. The youngest is a group of basic dykes, which 
are sometimes metamorphosed into true schist and sometimes 
remain unaltered. 
In Southern China old gneiss and schist that can be definitely 
attributed to the Fundamental Complex aresofarunknown. Schists 
and gneiss are reported te occur in the coast of Fu-kien ! among the 
igneous intrusions and extrusions. But sufficient data are not yet 
available for the determination of their stratigraphical position. 
(To be continued.) 
The Lower Carboniferous Chert Formations of 
Derbyshire.” 
By H. C. Sargent, F.G.S8. 
(PLATE IV.) 
INTRODUCTION. 
ae origin of chert has of late been discussed with renewed 
activity, especially in American scientific journals. Difference 
of opinion centres mainly round the question of the source of the 
silica ; whether it is of direct inorganic origin, or the result of the 
solution and redeposition of organic silica. Further points at issue 
relate to the age and formation of the chert; whether it is an 
original deposit contemporaneous with the country rock, or a 
metasomatic replacement of the latter and therefore of later age. 
The object of this paper is to discuss the evidence afforded by 
the chert formations of Derbyshire, and to state the conclusions 
which are believed to be indicated as to their origin. Such 
conclusions are, in brief, as follows :— 
(1) The cherts of Derbyshire are believed to be of direct inorganic 
origin, and not derived to any considerable extent, if at all, from 
organic silica. 
(2) They appear to have been mainly deposited contemporaneously 
with the country rock, and are not, except to a limited extent, a 
metasomatic replacement thereof. 
Rare occurrences are of later age. 
1 Tshil, “The Geology of the Yang-tze Valley’’: Bull. Imp. Geol. Surv. 
Japan, vol. xxiii, No. 2. 
* This paper is the substance of one read before the Geological Society of 
London, February 25, 1920, publication of which was declined (Abs. Proc. Geol. 
Soc. Lond., No. 1,051, pp. 47-8). Some additional evidence is now introduced. 
