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primary rocks whose uiolteii sands roso tirst .-iliovt' tlu' Itoiliug tioods and 

 cooled and crnsted into a cliaotie continent. For Arclinean ^ime com- 

 prised tliose millions of years which elapsed while the crust of the earth 

 'was cooling down to a roint where life was possible. 



The Laurentian locks are thus devoid of fossils or contain only the 

 remains of the simplest acpiatic forms. In North America they com- 

 prise the surface of a vast. \'-shaped area of 2.000,000 or more square 

 miles which lies, filled witii wild lakes, pine clad, rugged, almost impass- 

 able, spread in savage sleep from Labrador to the Arctic Ocean. This area 

 embodies the general f<niii of the North American continent and was the 

 nucleus of all the land which was afterward added to it. From these old 

 Laurentian rocks came the delnis and sediment which was laid down in 

 the bed of a shallow ocean to form the first rocks comprising the surface 

 of what is now "Indiana." 



At the close of the Azoic or Lifeless ?eon, during which the Laurentian 

 rocks were formed, the Paleozoic or ".Fon of Ancient Life" was ushered 

 in At its beginning the entire area of what is now known as Indiana 

 was covered by a liroad ocean Avhich stretched far away to tlie southwest, 

 while to the north and northeast it extended beyond the present sites of 

 the Great Lakes. This ocean is known to geologists as the 'Tnterior 

 Paleozoic Sea." Into it was carried the sediment derived from the erosion 

 and destruction of the old Laurentian rocks by water and air, which 

 agencies then, as now, were ever at work. The Potsdam sandstone of the 

 Cam1)rian era. wliicli prolial)ly underlies the Trenton limestone of the 

 Lower Silurian beneath the greater portion, if not all, of Indiana, was 

 one of the first strata to be laid down in this sea. But as n(Uie of the 

 surface of Indiana is represented by the I'otsdam stone, it will l»e passed 

 with this mere mention. 



Following the Cambrian came the second grand sub-division of I'aleo- 

 zoic Time, the so-called Lower Silurian or Ordovician Age. At its 

 beginning the sea covering Indiana and the area to the north and east 

 was of course more shallow, as 1,000 feet or more of Potsdam sandstone 

 had been deposited on its floor. The first great stratum of Ordovician 

 rock to be laid down in this sea which is of interest to us was the 

 Trenton limestone, which, during the past two decades, has lieconie so 

 noted in Indiana as the source of natural gas and crude petroleum. 



It is a well known geological fact that most, if not all. limestones owe 

 their origin to the presence of minute organisms in the water in which 



