SUMMARY OF RESULTS. 3 
Calciferous and Chazy Groups, is of special interest. The transition from 
the Cambrian to the Silurian fauna is very gradual, and such as would occur 
where there was no marked physical disturbance to influence the faunal 
change resulting from the natural dying out and development of species or 
the influx of new species from other areas. 
Of the species occurring below the passage beds three are identical 
with species occurring in the Potsdam sandstone of Wisconsin, viz: Hyo- 
lithes primordialis, Dicellocephalus Osceola, and Ptychaspis minuta; one with 
 Acrotreta gemma of the Calciferous formation of Newfoundland; and Pty- 
choparia Oweni is a common species of the Potsdam horizon in Montana 
and Dakota. These specific identifications and the great development of 
species of the genera Agnostus, Dicellocephalus, and Ptychoparia, in the 
middle and upper portion of the Cambrian section, furnish abundant evi- 
dence upon which to correlate the fauna and the geologic horizon at 
which it occurs with the Potsdam fauna and formation, as was done 
by Messrs. Hall and Whitfield (Geol. Expl. Fortieth Par., vol. iv, p. 
199, 1877). Of the Potsdam fauna eleven genera and fifteen species 
continue on into the passage fauna, viz (species of the Potsdam fauna 
are printed in italics): Lingulepis Mera, L. minuta, Lingula? manticula, 
Discina (sp. undt.), Acrotreta gemma, Schizambon typicalis, Obolella 
ambigua, O. discoidea, Leptena Melita, Orthis Hamburgensis, O. testudi- 
naria, Triplesia calcifera, Tellinomya ? Hamburgensis, Agnostus communis, 
A. bidens, A. Neon, Dicellocephalus finalis, D. inexpectans, Ptychoparia ? 
annectans, Ptychoparia affinis, P. granulosus, P. Haguei, P. Oweni, P. unisul- 
catus, Arethusina Americana, Amphion (sp. undt.), Barrandia McCoyi, Ile- 
nurus Eurekensis, Asaphus Caribouensis. 
In the next superior grouping, about midway of the Pogonip Group, 
all the middle Cambrian genera, with the exception of Orthis and Ilenurus, 
have disappeared, and higher up the genera Receptaculites, Cheetetes, 
Pleurotomaria, Maclurea, Cyphaspis, Bathyurus, and Asaphus carry the 
fauna up to the summit of the formation where the genera Receptaculites, 
Ptilodictya, Cheetetes, Strophomena, Orthis, Tellinomya, Modiolopsis, Ma- 
clurea, Cyrtolites, Orthoceras, Endoceras, Coleoprion, Leperditia, Beyrichia, 
Amphion, Ceraurus, and Asaphus give it a facies approaching that of the 
