:{i;:> The American Geologist. December. 1894 
exclusion of coajy substances. Since replacements or concen- 
trates are almost entirely confined to calcareous and siliceous 
rocks and those readily acted upon by metallic solutions.and sel- 
dom take a regular horizontal or definite and stable form, I, for 
one, would not accept such an explanation of these coal-seam 
shales. To suppose that such shale-bands were originally thin 
films of chalky mud. since chemically converted into silica, 
alumina, iron, etc., etc., would, I think, be exceedingly unsafe ; 
and yet the formation of widespread layers of something sim- 
ilar to chalk in composition at the present day (the "Globi- 
gerina ooze") over the bottom of the Atlantic ocean where 
deepest and farthest from land, would seem to furnish us 
with about the only way (as to physical conditions) in which 
our shale-binders in the "Pittsburg"' coal-bed can be imagined 
to have accumulated. 
(e) Precipitates. There occurs to me only one other known 
process or way hj which these binders could come into the 
coal ; it is on the supposition that the waters overlying the 
coal layers were so highly charged with minerals in solution 
that in the end there came a time when these were precipitat- 
ed as solid particles. Hence a sheet of uniformly-composed 
mineral ingredients was brought into existence and solidified 
where it lav. This theory makes these binders chemically- 
formed rocks. But, in my opinion, such an explanation of 
them will be rejected. 
Now, if the lower of these two slate-binders was really de- 
posited as a layer of fine silt or mud by the aqueous transpor- 
tation process, it becomes interesting to enquire: How was 
the succeeding or superimposed four-inch band of pure coal 
created or put there? for. in reality, it is abed of coal per se; 
and they who would regard coal-beds as remains of trees, etc., 
that grew where or near where the coal now is, with under- 
clays for their roots to meander and develop in, will have to 
consider this ^ to \ inch layer of shale as the urnlerbed of the 
four-inch layer of coal. I merely make this observation here 
to show how exceedingly cautious geologists should be when 
attempting to handle the subject of the origin of coal seams. 
Geological text-books don't seem to help us* one bit in try- 
ing to find a satisfactory explanation for the formation of 
anything so extensive, geographically, as these particular £ 
