212 BULLETIN OF THE 
Trenton Falls, as well as of several other species, is their very perfect 
state of preservation in a thin bed of limestone outeropping in a small 
ravine half a mile east of the Trenton Falls cafíon or gorge. An 
examination of the same horizon that this bed occupies, for several 
miles along the cañon, which is but half a mile away at one point, 
failed to give a single entire Trilobite, and the fragmentary remains 
are rare. Both above and below they are found, but not with any 
more of the animal preserved other than the dorsal shell and hypo- 
stoma. This shows that in the vicinity of the outcrop in the small 
ravine there is a limited area, which was surrounded by conditions that 
did not prevail elsewhere in that region, as the topography of the 
adjacent country permits of a close examination of the strata, and out- 
crops at the same horizon were examined in all directions in the vicinity 
for the purpose of finding other prolific localities. 
The layer of limestone on which the prolific layer rests is thick, and 
formed of the comminuted remains of Crinoids, Trilobites, etc., indicat- 
ing the action of shore waves and a distributing current. A change 
supervened, and this surface was depressed beneath deeper water, or a 
barrier reef was formed, affording a quiet habitat in which flourished 
Bryozoans, Echinoderms, Brachiopods, Pteropods, Entomostracans, and 
Trilobites. The remains of all these are now found, in a perfect state 
of preservation, attached to the lower surface of the superjacent layer 
of limestone. This appears to have been a deposit of fine calcareous 
mud or ooze, deposited on the surface of the subjacent stratum, so as to 
form when solidified a layer from one half to two inches in thickness. 
It did not destroy all the forms of life that existed on the surface be- 
neath prior to its deposition, but many species are not known to occur 
again. The Trilobites, however, flourished on the new surface as the 
beautifully preserved interiors of the dorsal shell testify, an illustration 
of which is given on Plate IV. 
Where the layer is over one inch in thickness, and there is no 
intermingled argillaceous shaly matter, as sometimes occurs, the best 
preserved specimens for cutting sections are found, They are usually 
with the dorsal surface downward, and partially enrolled. It was 
frequently noticed in polishing the sections that the imbedding rock 
showed dark laminations curving beneath the Trilobite, as though the 
soft mud had been compressed by its ‘sinking down into it. Similar 
traces proved that the mud flowed over into the half enrolled shell, and 
buried the appendages, or such as were left of them, as often the lami- 
nations of the inflowing mud have not been disturbed since covering 
the fragments of the viscera, branchiæ, and legs. 
