224 Reviews — American Oeoloyical Surveys, Iowa. 



The Coal-measures in America are not usually subdivided by 

 geologists, but are very naturally divided in Iowa into three portions, 

 Upper, Middle and Lovp'er — the latter containing the principal coal- 

 beds; but the two lower divisions composed of sandstone, shales and 

 thin beds of limestones. The upper portion is almost entirely a 

 limestone, without coal. It is in the south-west part of the State. 

 The general dip of the strata is south-westerly, with several 

 minor undulations. Hence the opinion of a synclinal structure, the 

 same limestones appearing in the valleys of the Missouri and Mis- 

 sissippi rivers, is no longer tenable, even though upheld by the 

 authority of Dr. H. B. Geinitz, in 1867. If Dr. White's identifi- 

 cations need revision, the upper limestone would be referred to the 

 Permian. Of that the reader may judge after the enumeration of 

 the fossils thus far discovered in it. There are among Selachian 

 forms the genera Cladodus, Diplodus, Petalodus, Chomatodus, Peri- 

 pristis, Petrodus, Helodus, Psammodus, and Deltodus ; of Crustacea, 

 Phillipsia, Beyrichia, and Cytherina; of MoUusks numerous Cepha- 

 lopods, Gasteropoda, LamellibrancJiiates, and Bryozoa, whose genera 

 are not mentioned ; of Brachiopods, the OrthidcB are represented by 

 Orthis, Meekella, Hemipronites, and Syntriclanna ; the Productidce by 

 Productus, Ghonetes, and Aulosteges ; the SpiriferidcB by Spirifera. 

 Mar tinia, Athyris, and Betzia ; Echinoids and Cyathocrinidse; Corals 

 by GampopJiyllum, AxopTiyllum, Zaphrentis, and Syringopora. Fusulina 

 composes rock masses, and AmpMstegina is present. The middle 

 division has six thin beds of coal, the largest two feet thick. The 

 lower division contains five beds of coal, from one to seven feet 

 thick. Of 64 samples of coal analysed, when undried, the average 

 percentages were these : of moisture, 8'57 ; of volatile combustible 

 matter, 39-24 ; of fixed carbon, 45*42 ; of ash, 6-77 ; total volatile, 

 47-81 ; total combustible, 84-66 ; coke, 52-19. When dried the 

 averages of the same samples were as follows : of volatile combus- 

 tible, 42-92; of fixed carbon, 49-70; of ash, 7-38; total combustible 

 92-62 ; coke, 52-08. The composition of the coke was 87-25 carbon, 

 12-25 of ash. 



The area covered by the outcrop of the Coal-measures is a little 

 less than half the State, and in no portion of it would valuable beds 

 of coal be found below 1000 feet from the surface. Hence Dr. White 

 suggests for the benefit of the people of the State, that future wants in 

 the direction of fuel can be easily supplied from their own territory. 



The " Mountain Limestones " of Iowa are well known on account 

 of the beautiful Crinoids abounding in the Burlington beds. Wach- 

 smuth's collection of them contains fifty genera and three hundred 

 and sixty-six species. The topmost member, the Chester Limestone, 

 is not found in Iowa. The Keokuk and Burlington Limestones dis- 

 appear in succession as one passes north-westerly, while the over- 

 lying St. Louis Limestone is persistent, and is found coextensive 

 with the Kinderhook beds. It therefore overlies the three members 

 beneath it unconformably. 



Near Fort Dodge is an extensive deposit of gypsum, with only 

 eight per cent, of foreign matters, which covers an area of about 



