38 



retained within them the oil and gas derived from their enclosed organic 

 remains. This oil. and its more volatile portion, the natural gas, was not 

 formed in a short time, but is the result of a slow decomposition or de- 

 structive distillation, carried on through thousands of centuries. Ac- 

 cumulating in vast reservoirs— the more porous portions of the Trenton 

 limestone or mother rock— it there remained until man came with his 

 iron drill and furnished a vent through Avhich it could rise. Then by 

 combustion he caused it to yield up the stored energy, conserved since 

 the sun's rays fell on the plants of the old Silurian seas. 



After the Utica shale had been laid down as a thick, impervious cover 

 above the Trenton limestone, there followed the Hudson River epoch 

 during which 200 to GOO feet of alternating beds of shale and limestone 

 were deposited in the old sea bottom where now is Indiana. These form 

 the uppermost division of the Lower Silurian age. During the myriads 

 of years necessary to their deposition marine forms were excessively 

 abundant and the advancement in the scale of animal life was corre- 

 spondingly great. All the principal groups of marine invertebrates which 

 came into existence during the Trenton epoch were represented, but the 

 species were widely different. In addition to life in the sea, there came 

 also to be life on land. Acrogenous plants— forerunners of the ferns and 

 mosses— harbingers of the vast forests of future centuries— came into 

 being along the moist waterways of the growing continent, while insects, 

 the first winged creatures, began to traverse the air. 



As yet no part of Indiana was above old ocean's level, but at the close 

 of the Ordovician, after the Hudson River limestones and shales had 

 been laid down, a great upheaval, caused by some subterranean force, 

 brought above the sea a large island of Ordovician rock which ever since 

 has been dry land. This upheaval was greatest over the point where 

 Cincinnati, Ohio, is now located, and the "Cincinnati Uplift" is the name 

 given by geologists to the island and the broad belt of shallowly sub- 

 merged land which extended from its northern shore in a northwesterly 

 direction, diagonally across the area of the future Indiana. The main 

 portion of that island comprised the southwestern corner of what is now 

 Ohio and a part of northeastern Kentucky. It also included a small part 

 of what is now Indiana and formed the first and oldest portion of the 

 surface of our State. The area whose surface rocks belong to this 

 Hudson River formation comprises part or all of Wayne, Union, Fayette, 

 Franklin, Dearborn. Ripley. Ohio, Switzerland and Jefferson counties. 



