IOWA ACADEMY OF SCIENCES. 
17 
near the middle of the formation it is composed of coarse, imper- 
fectly comminuted fragments of brachiopod shells cemented 
together, the spaces being filled with interstitial calcite. Among 
the recognizable species of shells Atrypa reticularis is the most 
common, but some beds contain very large numbers of Terebra- 
tula {Grancena) iowensis. At some horizons shells of an Ortho- 
thetes are common. Orthis impressa is not rare, and Rynclionella 
pugnus {Pugnax pugnus) occurs occasionally. The shells, or 
fragments of shells, making up the limestone are not embedded 
in a matrix. They are simply piled on each other and cemented 
together in a manner illustrated by the formation of the mod- 
ern coquina along the east coast of Florida. The rocks near 
the middle of the state quarry beds are a brachiopod coquina 
having the interstices completely filled with crystalline calcite. 
Near the middle of the formation the rock consists of thick 
ledges which, some years ago, were worked extensively. From 
these beds came the large limestone blocks used in the founda- 
tion of the new state capitol. Although the ledges show no 
definite lamination, and split as readily in one direction as 
another, the weathered surfaces on opposite sides of the num- 
erous joints often show obscure signs of oblique bedding. The 
material was evidently swept into place by moderately strong 
currents. 
The ledges worked in connection with the building of the 
new capitol are the heaviest afforded by the formation. The 
lowest one is four feet in thickness. It is made up of rather 
finely triturated brachiopod shells, the most common species 
being Atrypa reticularis. This bed, it seems, did not furnish 
satisfactory material for it was quarried only to a limited 
extent. The ledge furnishing the greater number of available 
blocks lies directly above the first. It is five feet in thickness, 
and is intersected by numerous joints. Among the great mul- 
titude of unrecognizable fragments of which it is chiefly com- 
posed it contains large numbers of entire detached valves of 
Atrypa and Orthothetes. The next ledge in ascending order 
to furnish usable stone is separated from the last by a talus- 
covered space of two or three feet. It also is five feet thick, 
and in it Atrypa and Terebratula are the prevailing brachio 
pods. In a fourth ledge, four feet in thickness, the reck is fine 
grained, the materials are very perfectly comminuted, species 
cannot be recognized, but it is evident that the bed is composed 
of debris from brachiopod shells mingled with triturated frag- 
ments of crinoids. Above the fourth ledge the layers yb^vj 
2 
