334 Editorial Comment. 
140 feet above present low water mark in the river. 
This and another deposit he says has been referred to the 
Terrace epoch. There may be no connection between this and 
the fissure deposit in the rocks across the river and elsewhere, 
but the carbonaceous material seems similar. I have found no 
mention of these cavities or fissures in the Illinois reports 
though the}'^ are known to exist in quarries in Whiteside coun- 
ty and among the lead mines about Galena, and may occur else- 
where. 
Note. — In tke second annual report of the Minnesota survey, 1873, are 
described several pockets and cavities excavated in tlie Silurian limestone 
at Manliato, Minn., filled with what was taken to be Cretaceous clay. 
Since then the Cretaceous has been found filling cavities and fissures in the 
Devonian at Austin in Mower county, and at LeRoy in the south-eastern 
part of the same county near the Iowa state line. Cretaceous deposits, in 
fiitu, have been found widely distributed in the southern part of the state. 
They contain fossil leaves that are referred by Dr . Lesquereux to the 
Dakota group . In a similar manner Cretaceous deposits are described 
as filling gorges in the older rocks in Missouri and in Southern Illinois. 
Circumstances point to the Cretaceous as the probable age of the clay 
above described by Mr. Farnsworth. The fish teeth, the carbonaceous 
matter, the white sand (same as at Austin) the fossil wood, the fire-clay 
quality, are all characters that appertain to the Cretaceous in Minnesota. 
A microscopic examination might reveal characteristic foraminifera. 
N. H. W. 
EDITORIAL COMMENT. 
FoEMATioN OF Coal Seams. 
W. S. Gresley, Esq., F. G. S., publishes in the Quarterly 
Journal of the Geological Society for November, 1887, a paper 
in which he attacks the '■'' growth- iii-situ theory" of the forma- 
tion of coal. He says that the advocates of that theory ad- 
here to it because, (1) "the accumulation of the vegetable mat- 
ter of coal beds by driftage appears to be totally beyond our 
comprehension, (2) we have been told and led to believe that 
the underclays of the coal seams contain the Stigmariae which 
were the very roots of the trees, the remains of which consti- 
tute the bulk of the coal.'' 
If it be true that we must accept either growth in situ or 
driftage, with no possible third alternative, then the first of 
