¥ sag eer 8 
De She ar 
~ = " ~ 
' a 476 
660 - STRATIGRAPHICAL GEOLOGY. — [Boox VI. 
Texas, and Georgia. Westwards from the great valley of the Mississippi, 
where they have been found in many places, they reappear from under 
the Mesozoic and younger Paleozoic rocks of the Rocky Mountains. 
They have been divided by American geologists into two formations— 
(1) Acadian, a mass (2000 feet) of grey and dark shales and some sand- 
stones; and (2) Potsdam (or Georgian), which attains in Newfoundland 
a depth of 5600 feet, but thins away westward and southward till in the 
valley of the St. Lawrence, where it was studied by Logan and his 
associates of the Geological Survey of Canada, it is only from 300 to 600 
feet thick. 
Among the organic remains of the North American Cambrian rocks 
fucoid casts appear in many of the sandstones, but no traces of higher 
vegetation. The Acadian formation has yielded primordial trilobites of 
the genera Paradoxides, Conocoryphe, Agnostus, and some others ; brachio- 
pods of the genera Lingulella, Discina, Obolella, and Orthis; and several 
kinds of annelide-tracks. The Potsdam rocks contain afew sponges, the 
earliest forms of graptolite, some brachiopods, including, besides the 
genera in the Acadian beds, Obolus, Camarella, and Orthisina; some 
pteropods (Hyolithus or Theca); two species of Orthoceras ; annelide- 
tracks; trilobites of the genera Conocoryphe, Agnostus, Dikelocephalus, 
Olenellus, Ptychaspis, Chariocephalus, Aglaspis, and Illenurus. Some of 
these genera ascend into the base of the Silurian system, but Aglaspis, 
Chariocephalus, Illenurus, Olenellus, Paradoxides, Phemphigaspis, and 
Triarthrella are confined to the Cambrian zones. 
M. Barrande has called attention to the remarkable uniformity of 
character in the organic remains of his primordial zone over the con- 
tinents of Kurope and America. He published eleven years ago the sub- 
joined table, to show how close is the parallelism between the proportions 
in which the different classes of the animal kingdom are represented. 







Crustaceans. Molluscs. nd 
3 tc} 
Countries. 3 legged Dee Z 
EA DB a 4 a A 3 3 A wn 
2/5/ 3/3! 2] 8] &| &| 3] 8! ¢| 2 
Si5/s/3| S| 8)8/ 4 )8/8) &l ¢ 
= /8|8/)8| 2/818) 21 Beles 
BH |/6| Oo] 4d] & | I co | ey ee ee 
ew ree, ee PP ire ——|—| |_| —|__ 
1. Bohemia . 27 we 5 ca |. ea es 46 
2. Spain. Sat ALS des Ae 9 1 sf 2/ 6 uf 19 
3, Scandinavia { Pee \ .| 77 5 2 814 96 
ma Menevian 
4. England {Wrenewie ‘aisth | BBA adog oy 6 1| 2/58 
5. Newfoundland . . . 2 | on 9 
6. New Brunswick 18 os 6 1 95 
7. New York moe, S 5 ste 5 
8. Braintree (Massachusetts) . 1 es al col 
172/1/10|4/14|../2| 28/518] 2=246 







' Trilobites, Prague, 1871, p. 195. Since the publication of this table the progress of 
research has increased the number of species from most localities; but the general 
facies of the primordial fauna has not been materially affected thereby. 

