GEOLOGY OF LA GRANGE COUNTY, INDIANA. 29 



This age is divided into three periods ; named in the order of formation : 

 Triassic, Jurassic, and the Cretaceous or Chalk period. 



It is presumed that the reader is cognizant of the origin of the above names, 

 but, to make the point more plain to the general class of readers, I will explain 

 the meaning of the terms. 



The Triassic (triple), takes its name from the fact that in Germany it is 

 composed of three distinct groups. The Bunter Sandstein or colored sandstone, 

 the Muschelkalk or mussel chalk, a miner's term, meaning a group of red and 

 green marls and shells. It is sometimes termed the new Red Sandstone, to dis- 

 tinguish it from the old Red Sandstone of the Devonian. 



The Jurassic period derives its name from the Jura Mountains, on the west- 

 ern borders of Switzerland, one of the regions characterized by the formation. 



The Cretaceous period derives its name from the Latin creta, chalk. The 

 chalk, of England and other portions of Europe, is one of the rocks of the 

 period. Says Prof. Dana, "The Triassic continent spreads westward to Kansas, 

 and southward to Alabama. While on the east, the continent probably stood 

 above its present level, through this period, and while, over much of the .Rocky 

 Mountain region, the land was barely emerging from the waters, or was covered 

 by interior salt seas, farther west, over a large part of the Great Plateau, and the 

 rest of the Pacific slope, the surface was washed by the Pacific and peopled with 

 its life. The Sierra Nevada was then no barrier to the ocean ; for the sands, 

 mud, and limestone accumulated in those waters, constitute some of its rocks. 

 The stratified beds of the mountains were then in the progress of formation, 

 through the action of the Pacific tides, currents, and waves, and the growth of 

 marine life. The making of the Sierra was delayed till the rocks of still another 

 geological period had been deposited upon the Triassic." 



The fossils of this period are not abundant in this vicinity. I will, however, 

 mention a few only. Of the Cephalopods : the ceratitcs nodosus, a quaint-looking 

 fossil, resembling more nearly a long, tapering worm rolled up into a wheel, the 

 smallest part being rolled into the center. Specimens of the Orthoceras — similar 

 to the Devonian type — are to be found occasionally. Ostracoids : esiheria minuta, 

 a very small shell-animal, ] which must have been an easy prey to the many 

 monsters then inhabiting the Triassic Sea. With this small list of fossils, which 

 is all that I have been able to identify, I pass to the Jurassic period. Its plants 

 were mostly of the land and were mainly ferns, conifers and cycads, something 

 like the Triassic. I have in my possession a fossil containing some of the stems 

 of the ferns of this period. 



The animal life of this epoch is quite well represented in the rocks of this 

 region. Oolites sponge — scyphra reticulata were the most abundant of this fam- 

 ily. Of the Polyp Corals of the Oolite, Montlivaltia caryophy llatz. and Prionas- 

 traea oblonga, two corals resembling somewhat the Polyps of the Devonian and 

 Silurian periods. Of the Lamellibranchs of the Lias, the Leptaena Moorei and 

 Spirifer Walcotti; and of the Oyster family of the Oolite, Ostrea Marshii, 



