472 Reviews — The Geology of Illinois. 



These volumes sketcli first the physical geography, and then the 

 general geology of the State, describing each formation in turn, in 

 the descending order. After this are essays upon the Lead Eegion, 

 Coal Fields, and Plants, Origin of Prairies, etc., and a list of chemical 

 analyses. All the fossils are fully described and well figured. The 

 chief bulk of the volumes is made up of detailed descriptions of 

 the special geology of fifty-five of the counties. In the Palceonto- 

 logical portion the description of the Coal-Measure Plants occupies 

 178 pages and 46 plates — :256 species. Only one Eeptile, a Batrachian, 

 has been found. The Fishes are described upon 155 pages and 17 

 plates. The Invertebrates of the Carboniferous system occupy 401 

 pages and 26 plates — MoUusks and Crinoids being the most abundant. 

 The other classes are Insects, Crustacea, Myriapods, Annulata, 

 Echinodermata, Gasteropods, Lamellibranchiates, Cephalopods, Bra- 

 chiopods, Polyzoa, and Sponges. The fossils from the Trenton to 

 the Hamilton group are described upon 159 pages and 13 plates. 



The following is the nomenclature of the formations given in the 

 Becond volume, which is an improvement upon that issued earlier : 



Maximum Thickness in Feet. 



Post- Tertiary. Modified Drift and Drift 150 



Tertiary. Eocene? 150 



Upper Carboniferous. Coal-Measures and Millstone Grit... 1000 



f Chester Group 800 



^J r^.„-,„ „„ 71^ ^ • St. Louis Beds 200 



5 s Lower or Mountain J xr i i ri i ca 



ol Limestone < Keokuk Group 160 



o d^imestone. ] Burlington Group 200 



■^ l^Enderhook Group 150 



^ Genesee Slate 100 



g I Hamilton Beds 120 



o ]^ Upper Helderberg Limestones 25 



B Upper and Lower Oriskany Sandstones 240 



'Lower Helderberg Limestone 200 



Niagara Group 200 



Cincinnati Group 140 



Galena and Trenton Limestones 300 



St. Peter's Sandstone 150 



j^Calciferous Division , 120 exposed. 



Illinois contains 55,400 square miles, extending over five degrees 

 and a half of latitude. The entire western border is the Mississippi 

 Eiver, and hence the general slope of the surface is south-westerly. 

 The country is essentially a plain, with a few mounds about 1150 

 feet above the sea in the north-west part, which are elevated 200 to 

 250 feet above the general level or prairie. The strata show five 

 lines or axes of disturbance — usually faulted — sometimes an anti- 

 clinal axis. The line of disturbance varies from W. 10° N. to N. 20*^ 

 W. In one case the St. Peter's sandstone and Burlington limestone 

 are made to face each other, the downthrow being nearly 1500 feet. 

 The epoch of disturbance was Post-Carboniferous. 



All the State is covered by the ice-drift, unless a "mountain 

 chain," from 500 to 600 above the mouth of the Ohio Eiver, 

 limits it upon the south. A part of the N.W. area is included in 



