212 BULLETIN OF THE 



Trenton Falls, as well as of several other species, is tlieir very perfect 

 state of preservation in a thin bed of limestone outcropping in a small 

 ravine lialf a mile east of the Trenton Falls canon or gorge. An 

 examination of the same horizon that this bed occupies, for several 

 miles along the canon, 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, branchiae, and legs. 



