245 



with more or less heavy spar, the whole capped by a bed of crys- 

 talline heavy spar, including galena. The 3d Magnesias limestone 

 is also metalliferous, and holds in drusy cavities crystals of pyrite 

 and chalcopyrite. It sometimes contains more than the proportion 

 of magnesian carbonate required to form dolomite, a not very 



The coal measures of the state, belonging chiefly to the great 

 western coal-fleld, and occupying an area of nearly 23,000 square 

 miles, are described by Mr. Brodhead with much detail. The 

 coal seams are generally thin, though some in the lower measures 

 occasionally attain four feet. Their local value is very great 

 from the scarcity of wood, and we are told in one place of a seam 

 of from ten to fourteen inches which is wrought, the coal being 

 sold at the mine for twenty cents a bushel. In regions where the 

 product commands so high a price even small seams are precious. 

 The coal deposits of Lincoln county in the eastern part of the 

 state, belong, unlike those just referred to, to the central or Illinois 

 field, and present the unusual character of detached basins of coal, 

 sometimes twenty-five feet in thickness, with little or none of the 

 usually accompanying strata, occupying depressions or previously 

 excavated basins in the Lower Carboniferous limestone. These 

 basins are very limited in extent, and have but a local importance. 



The discussions of the various points with regard to the eco- 

 nomic geology of the state, the chemical investigation of its iron 

 ores, and the valuable appendix or investigations on the strength 

 □g materials, all of which show good and thorough work 

 alike for science and for the material advancement of the state, 

 would occupy too much of our space. Since the regretted resigna- 

 tion of Prof. Pumpelly, on account of ill health, the direction of 

 the survey has been confided to Mr. Brodhead, whose report for 

 1873, we have just received and shall soon notice. The beautiful 

 atlas of maps which accompanies the report of 1872 should not 

 pass unnoticed. These maps are from the establishment of Mr. 

 Julius Bien of New York, who, by the admirable style of his 

 work, has put all students of geology and geography under obli- 

 gations to him.— T. S. H. 



Relation of British Will F..owi:us In>f,W— The author 



