Review of Reent Geological Literature. 271 
remain where they fell, but some may have had just the right 
lightness and the right shape to be rolled over the bottom by the 
currents in the water. Filamentous algje and other organic bodies 
may have helped to form them. Once started, such a cluster 
would pick up fragments that happened to lodge in the interstices 
among its particles, first larger ones and then smaller. Thus the 
pellet would grow and form a crust of finer material than that in 
the nucleus. 
If such is the correct explanation of the formation of these 
structures, similar ones may be looked for in other places, where 
there is evidence of wave motion and of rapid sedimentation (for 
it seems that both of these are requisite conditions), whenever the 
material is of such a nature that its particles are apt to get tangled 
up with each other. Thin flakes are evidently more apt to form 
clusters in this way than rounded grains of sand. It may be of 
interest to mention in tliis connection that pellets, apparently of a 
like kind, have been found in ripple-bedded places in the micace- 
ous shales, or sandstones, which make the famous fossil-bearing 
beds on Mazon creek, in Grundy county, Illinois. 
Augustana College^ Rock Island, Ills. , Jan. 28, 1893. 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
A preliminary report on the Coal Deposits of Missouri. By Arthur 
WiNSLOAV, State Geologist. Geological Survey of Missouri, Jefferson 
City, November, 1891; 226 pages. — This is the first of a series of subject 
reports published by the Missouri survey; two others, one on Iron Ores, 
and another on Mineral Waters, have already been issued.* The report 
is written in a semi-popular style, but is nevertheless of scientific inter- 
est and importance. It is intended, primarily, as a statement, which 
shall be easily accessible, of what is at present known concerning the 
coal deposits of the state. The questions of the correlation of the dif- 
ferent coal beds and a general discussion of the stratigraphy of the 
Coal Measures are necessarily but briefly touched upon, or omitted. 
That part of the report which is of special interest to the citizens of 
Missouri is "A systematic description of the coal beds now operated." 
This occupies more than one-half the report, and brings together a 
large amount of detail concerning the difterent pits in workable beds 
of coal. One of the special features of this part is the large number of 
detailed sections of the strata immediately above and below the coa* 
*Reviewed in the last (Jeologist. 
