GEOLOGY OF TEE WEST. 4S'J 



level of the Mississippi river and the i^avements walked by the busy popu- 

 lation of St. Louis, once rolled the waves of the silurian ocean. 



We will suppose this auger hole is a shaft 6 by 10 feet square from the 

 surface to the bottom of the hole, and that we have the innvilegc of going- 

 down and examining the strata in its sides as they would appear from the 

 records shown by the borings as the auger penetrated the strata. 



First we pass 20 feet of alluvial brick clay, then 40 feet of pipe clay, 

 shaley limestone and fire clay, and at 60 feet deep we find a three foot vein 

 of coal; at 200 feet wo reach the upjoer Archimedes limestone, the same 

 stratum that is exposed at the top of the deep quarry on Tayon avenue, and 

 which contains fossil fish ; this is also the same ago of rock as the Grafton 

 quarry. Below this is the St, Louis limestone, and next another floor of 

 lieokuk or archimedes limestone, a rock filled with fossils. At 1,200 

 feet we reach the great salt and oil floors of the Mississippi basin. This 

 stratum comes to-day 30 miles below on the I. M. and S. E. E., and west 30 

 miles on the M. P. E. E., and from a quarry south of the city that furnished the 

 rock to build the basement of the Four Courts : and as that rock weathers, 

 its black, mottled color is due to the bitumen which the heat of summer 

 has brought to its surface. Chicago is built on this geological horizon, and 

 strata in quarries west of that city are filled with bitumen and petroleum. 

 If space would admit, we might trace this floor throughout the length and 

 breadth of the great basin of the Mississippi, and show where it rises 

 to-day ; and has again gone down 4,000 and 5,000 feet under the coal meas- 

 ures of the grand prairies of Illinois and Kansas, and is formed in a great 

 basin in Venango county, Pcnn., and this again subdivided in lesser basins, 

 and where the economic laws had stored the rich floors of petroleum that 

 have proven such a source of national wealth. But wo must go downward. 

 At 2,000 feet we have reached the Niagara group of the upper silurian series, 

 .a rock rich in fossils, and of the same age as that over which the great cata- 

 ract pours its thundering falls. This rock also forms the table lands of 

 Iowa, west of Dubuque, and is the formation of the maramillary outlj'ing 

 mountains that make such a conspicuous feature in the topography of the 

 iipper Mississijopi lead flelds, also forms the mound system of the great lead 

 and zinc fields of Central Missouri. Below this we reach the "Trenton lime- 

 stone," a member of the silurian sj'stem, and same age of rock as found 

 shelving out at low water mark on the Mississippi opposite Dubuque, Iowa, 

 and where the weathering of the slabs has exposed in an embossed form the 

 tribe of the orthosceratites. These fossils are there seen six and ten feet in 

 length, and with their enameled scales and bucklers were the mailed war- 

 riors of the silurian seas. Below we find the lower floors of the lower silu- 

 rian, chert-beds, hornstone and coralline limestone, the same age of rocks as 

 that which abuts against the Iron Mountain on its west side, and is the great 

 lead, zinc, copper and iron-bearing rock of South-east Missouri. In passing 

 the Archimedes floor in the subcarbonifcrous system, we were in the hori- 

 zon of strata that carries the g-reat lead and zinc veins of South-vrest Missouri. 



