50 



solvents and abraders — its work of a day, a year, a century, upon the 

 solid limestone not appreciable to the eye— yet by slow unceasing action 

 through the ages which have elapsed since that limestone was raised 

 above the sea, it has carved every room and passage, constructed every 

 pillar and stalagmite existing beneath the surface of southern Indiana. 



The Huron limestone or Huron group of rocks represents in Indiana 

 the latest epoch of the Lower Carboniferous Era. It is composed of 

 three beds of limestone with two intervening beds of sandstone, their 

 combined thickness being about 100 feet. The sandstones carry in places 

 concretions of iron ore and thin beds of coal, the latter being the fore- 

 runners or harl)ingers of those vast veins of stored energy which, in 

 southern Indiana, represent the Carboniferous and tinal era of Paleozoic 

 time. 



The Carboniferous Era is noted as one of gentle oscillations in the 

 surface of those shallow seas bordering the land, these "causing suc- 

 cessive moi-e or less wide emergencies and submergencles, the former 

 favoring the growth of boundless forests and jungles, the latter burying 

 the vegetable debris and other terrestrial accumulations beneath fresh 

 water or marine deposits." 



During the era, that cryptogamous land vegetation which had sprung 

 into existence in the Devonian Era, advanced with wonderful strides. 

 The temperature was mild: tne atmosphere moist and heavy laden with 

 carbon dioxide. As a result the vast lowland marshes were overgi'own 

 with great trees of Sigillaria, Lepidodendron and Calamites; while at 

 their base grew dense thickets of fern underbrush, inhabited only by 

 insects and amphibians. For the first examples of the latter evolved 

 during this period from some mud-loving, fish-like creature. No flow- 

 ering plant had as yet unfolded its petals. No bird had, as yet, winged 

 its way through the buoyant air. No mammal was, as yet, a denizen 

 of earth or sea. Those dim watery woodlands were flowerless, fruit- 

 less, songless, voiceless, unless the occasional shrill of a cricket or grass- 

 hopper could be called a song. Yet in the cells of the semi-aquatic 

 plants and trees of those old forests there was stored that heat which 

 was destined in after ages to be freed by man and used in doing the 

 work of the world. 



The rocks laid down during this era were alternating beds of sand- 

 stone, shale, clay and limestone with occasional beds of compressed 

 vegetation which, during after centuries, has been changed into coal. 



