ii6 Ediwrial Ccmment. 
over all the area at once; that only a comparative! v narrow belt 
is occupied by living corals at any given time, and hence suc- 
cessive, narrow, parallel areas of the entire region had to be 
conquered and filled up one after another. The amount of 
calcareous matter dissolved and carried away falls but little short 
of the amount secreted. The operations, furthermore, are not 
only of stupendous magnitude, but they certainlv increase im- 
measurably our conceptions of the length of the modern geolog- 
ical period. Here are species and here also are conditions that 
must have remained practically unchanged since the operations; 
began. 
As we said before, geologists atid scientists generally will 
content themselves with one question. Is the theory in accord 
with demonstrable facts ? 
ON THE CHERT OF THE UPPER COAL MEASURES Ix\ MONT- 
GOMERY COUNTY, IOWA. 
The discussion of the organic origin of chert, by Dr. G. J. 
Hinde, in the Geological Magazine for October, 1S87, suggest- 
ed the propriety of re-examining the chert in the Upper Coal 
Measures of low^a. The chert is particularly alnmdant in the 
Upper Carboniferous limestones of Montgomery count}', the 
geological horizon being about the same as that at which Dr. 
Hinde procured his specimens in Ireland, North Wales and 
Yorkshire. The chert from the Carboniferous limestones of 
Great Britain and Ireland proves to be composed largely of 
sponge spicules, practicallv imchanged, and Dr. Hinde con- 
cludes that it is not a pseudomorph that has taken the place of 
calcareous matter. Occasionally fragments of crinoids, chang- 
ed to silica, are found in the British Carboniferous chert, but no 
foraminifera were observed. 
The Iowa Carboniferous chert differs from that examined by 
Dr. Hinde in being often crowded full of shells of foraminifers 
belonging to the species FHSidhia cylindrica. These shells 
are all completely silicified, and, at least to the extent that they 
make up the mass, the Iowa chert is pseudomorphic. Micro- 
scopic sections were prepared and carefully examined, but no 
indications of sponge spicules were detected. Examination 
