FOPULAR EXPLANATION. 17 



of the State Hospital for the Insane, at Mt. Pleasant, who 

 presented a series of carefully preserved specimens of the 

 borings of their artesian well, the knowledge we had before 

 obtained of the order of superposition of the formations was 

 very satisfactorily corroborated. An examination of these 

 enabled us to identify by their lithological characters, the 

 formations which the drill passed through, because we were 

 previously acquainted with the character of those formations, 

 by having studied them as they successively make their 

 appearance to the northward. The record of that boring says 

 that the drill passed through no coal. This could have been 

 predicted, because the work was commenced upon the surface 

 occupied by the sub-carboniferous limestone, which of course 

 underlies the coal bearing formations, as its name implies. 

 If they had commenced the boring in Jefferson, the next 

 county to the westward, they would doubtless have passed 

 through at least a portion of the coal measure strata before 

 the drill reached the limestone formation upon which they 

 began to bore in Henry county. 



From what has thus far been said, it will be seen that the 

 general dip of all the formations of the State is to the south- 

 ward and westward, but more nearly in the former direction. 

 This general dip is so slight that it is never perceptible to the 

 eye, and any dip of Iowa strata that is so perceptible, may 

 be regarded as a local dip only, and will be found to change 

 within a short distance. This general dip of all the forma- 

 tions to the southward and westward has one exception, 

 namely, the Cretaceous strata. These occupy a considera- 

 ble portion of northwestern Iowa, and have a general dip to 

 the north of westward, but it is a very slight one. 



These remarks apply thus far to the stratified rocks only 



which form the foundation, so to speak, of the State, but 



which are very generally covered from sight beneath the soil 



and subsoil. Geologists are almost entirely agreed in the 



opinion that after all the stratified rocks had been formed, 



there was a time when the whole northern hemisphere as far 

 3 



