64 
IOWA ACADEMY OF SCIENCES. 
of the exposure. The stratum from the point of best exposure 
dips to the west, and, so far as I could observe, can be followed 
in that direction no more than twenty or thirty rods when it 
dips below the present level of the excavation. Eastwardly it 
thins out, and at length becomes only a trace, obscure, or van- 
ishes entirely. For the greater part of the entire distance the 
structure and composition of the bed varies from rod to rod, 
but everywhere where the exposure is thickest the purity of 
the seam is greatest below. Indeed, in the most favorable 
case examined the purity of vegetable accumulation near the 
bottom of the formation is remarkable in the extreme, there 
being no admixture, so far as can be discovered, of any other 
substance whatsoever. 
Upwards the materials are less pure, the amount of inorganic 
matter increasing until the seam blends above with the over- 
lying blue clay or drift. It is a little surprising to find the 
lowest, that is, the oldest part of the bed, exhibiting organic 
objects in most perfect condition. The bottom of the seam is a 
compact mass of moss, compacted and pressed together no 
doubt, but absolutely untouched by putrefaction or decay, per- 
fect in every leaf and fibre as any herbarium specimen in the 
world. Specimens you may examine show this perfectly. 
You may see the stem, the attachment of the leaves, the inno- 
vations, the form of each leaf, nay, the very areolation of leaf 
apex and base, quite as absolutely defined as in the case of any 
freshest specimen one may bring in now from any living turf 
or forest bed. For this reason we are able with much confi- 
dence to identify the species concerned although, so far, we 
have seen no smallest sign of capsule or fruit. So far, also, all 
the material seems to represent but a single species, Eypnum, 
probably Hypnum Huitans Linn. , a common moss which creeps 
out from shore or clings to fioating objects, itself immersed or 
semi- floating in ponds, marshes or peat- bogs around the whole 
northern world. 
Above the compacted moss which altogether makes up an 
inch or two of solid matter, lies a still more solid mass of vege- 
table detritus several inches thick. In this case the vegetation, 
whatever it was, appears to have undergone pretty thorough 
decomposition and disintegration before it was compacted. 
The microscope reveals simply cells and fragments of cells 
with considerable admixture of sharp, white sand, but nothiag 
identifiable. This pulpy layer blends rather abruptly above 
