Mesozoic and Cenozoic Geology and Paleontology. 25 
of the greatest abundance of Leda truncata, the most exclusively 
Arctic shell of these deposits. In other words, he regarded the plants 
above mentioned as probably belonging to the period of greatest re- 
frigeration of which we have any evidence—of course, not including 
that mythical period of universal incasement in ice, of which, in so 
far as Canada is concerned, there is no evidence whatever. 
The Tertiary formation * exists in the southern part of the State 
of Illinois. It is best developed in Pulaski and Massac counties. 
It is represented by a series of stratified sands and clays of various 
colors, with beds of silicious gravel, often cemented into a ferrugin- 
ous conglomerate by the infiltration of a hydroxyd of iron. In some 
places it contains green, marly sand, with casts of fossils, and along 
the edge of the Ohio, at extreme low water, at Caledonia, there is a 
thin bed of lignite. At Fort Massac, just above Metropolis, the fer- 
ruginous conglomerate is from forty to fifty feet in thickness. Near 
Caledonia, a section gave a thickness of 564 feet. 
T, A. Conrad+ described, from the Miocene of the Eastern and 
Southern States, Nassa subcylindrica, Volutifusus typus, Cancellaria 
scalarina, Saxicava parilis, Spisula capillaria, Tellina peracuta, T. 
capillifera, Astarte compsonema, Lithophaga subalveata, Macoma 
virginiana, Mercenaria obtusa, and Cumingia medialis. | 
Philip P. Carpenter{ described, from the Pliocene of Santa Barbara, 
California, Turritella jewetti, Bittium armillatum, Opalia insculpta, 
Trophon tenuisculptus, and Pisania fortis. 
In 1867, Prof. E. W. Hilgard§ said that nowhere has the geologist 
more need of divesting himself of reliance upon lithological characters, 
than in the study of the Mississippi Eocene. Not only do the materials 
of the different groups often bear a most extraordinary resemblance to 
each other, but their character varies incessantly, in one and the same 
stratum, within short distances. Hale remarks that in Mississippi, 
the Orbitoides limestone seems to be represented by blue marlstone, 
and so itis, sometimes. But while on the one hand we see the hard 
limestone of the Vicksburg bluff passing into blue marl (Byram, 
Marshall’s quarry ), we on the other hand find it passing equally into 
a rock undistinguishable from that of St. Stephens (Brandon, Wayne 
county) ; the varied fossils described by Conrad disappearing almost 
= Geo. Sur. of Tll., vol. 1. 
+ Am. Jour. Conch., vol. ii. 
tf Ann. & Mag. Nat. Hist., 3d ser., vol. xvii. 
§ Am. Jour. Sci. & Arts, 2d ser., vol. xliii. 
