168 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
represented in the rocks accessible to us? Nearly all the known Silurian 
Crinoids come from the outcroppings of the strata at two localities in Europe, 
and three or four in America. The Devonian exposures producing well 
preserved specimens are even more limited. The Lower Carboniferous col- 
lections are better and more widely distributed, but are insignificant after 
all. Take the Burlington and Keokuk limestones, which in a few localities 
have produced more Crinoids in number and species than any other forma- 
tion. They consist of several hundred feet of strata almost entirely composed 
of the comminuted remains of countless myriads of Crinoids — fragments 
which are worthless to the Paleeontologist. It is only rarely that a thin 
layer is found in which the calcareous skeletons are preserved well enough 
for study ; — little basins of limited extent, in which, during a period of tem- 
porarily quiet waters, the Crinoids lived, died, and were imbedded at suffi- 
cient depths to escape the detructive effects of shore action. If the collector 
happens to be present when one of these colonies is uncovered by the 
quarrymen, the specimens may be rescued for the benefit of Science. But 
it is an even chance that they will be buried in the debris of the quarry, 
broken up for ballast, or walled up in the foundation of a building, and thus 
be lost again. Out of the thousands of square miles in which these rocks lie 
nearest the surface, all the collections that have ever been made represent 
only the imperfect gleanings of not more than a few acres. If it be sup- 
posed that we get, even in this way, a fair representation of the crinoidal 
life of that period, the answer is that almost every new discovery of “nests” 
or “colonies” of good specimens brings to light new forms, and that species 
or genera hitherto very rare are often suddenly found within a limited space 
quite abundantly. In the Upper Coal Measures, to judge from our books 
and museums, one would suppose that Crinoids were well-nigh extinct. 
Scarcely a dozen species are known, and most of them only by their lower 
calyx plates. Yet there are many beds in this formation which extend over 
hundreds of thousands of square miles from the Missouri Valley far into the 
Rocky Mountains and tilted up along their flanks, which are completely 
filled with fragments of Crinoids. Suddenly the collectors at Kansas City, 
who have studied these rocks for years, discover an abundant deposit of well 
preserved specimens in a shale so soft that a few minutes rain dissolves 
them into unrecognizable fragments. 
The importance of these observations, as a practical matter, is sufficiently 
shown by the fact that the discovery of a single specimen may sometimes 
