Artesian Well Borhuj in Southeastern Minnesota — Hall. 129 



Minnesota may in general terms be said to be on the east the 

 eastern boundary of the state, on the south Iowa, and on the north 

 and west a line from Iowa to Duluth, so drawn that it would pass 

 through New Ulm, Elk River and Hinckley. Very likely in the 

 northern part of this territory the Cambrian rocks stretch beyond 

 Anoka and Hinckley; that area is not yet fully explored. These 

 rocks are made up of alternating sandstones, shales, limestones 

 and dolomites, whose position is nearly horizontal. Again, no 

 profound movements of the earth's crust have occurred here in 

 the northwest since these rocks were laid down as Cambrian and 

 Silurian sea sediments; therefore no shattering of the rocks has 

 produced great fissures through which streams of water may 

 escape. 



Therefore, any water settling down into the porous portions 

 of these strata naturally seeps along for great distances without 

 passing to a level greatly lower than that which it strikes when 

 first starting on its underground course. These sandstones, shales 

 and limestones* vary in thickness from thin, interstratified beds 

 to formations hundreds of feet in thickness. They vary, too, in 

 composition in different portions oi the state. The limestones in 

 places become shaly, and the shales give place to sandstones as 

 the beds are followed from one end to the other, or more exactly, 

 as one follows the beds from the southeastern corner of the state 

 towards the north and west, where the formations thin out and 

 f^ive place to the Archean rocks of the upper Mississippi and Min- 

 nesota river valleys. 



Yet rao.^t o£ the formations are very persistent. The sand- 

 stones and the limestones which are exposed along the river 

 u:orges can be followed from one gorge to another, or from one 

 deep well to another, over nearly all southeastern Minnesota, and 

 are known to occur in Wisconsin and Iowa. The sandstones are 

 the waterbearing strata, and this persistence is important to the 

 well borer. It enables him to calculate to a very close figure the 

 depth in any part of this area to wliich he must bore in order to 

 reach a formation that everywhere, according to experience, 

 yields an abundant supply ot* watc. 



*The term ''limt'stone" is usod lien^ in its generic rather tlitiu in its 

 speeitif sense to include the carbonates. .Strictly speaking, a limestone is 

 a carbonate of lime, or, more modern ly expressed, a calciuni carbonate. The 

 Silurian carbonates of Minnesota contain magnesium carbonate in amount 

 Irom 5.40 per cent. (p. 120) upwards, while tlie (/ambrian carl)onates are in 

 l>laces almost tyi)ical dolomites, and no where are they free from considera- 

 ble magnesium carbonate. 



