IOWA ACADEMY OF SCIENCES. 33 



D's. Its present conceptions are due to careful balancicg of 

 ever accumulating evidence. In probably no other science has 

 there been so much shifting of opinion, and none can vie with 

 it in the amoutit of wreckage of abandoned theory. 



In the short five minutes at command, i o more can be done 

 than to state the condition of the science one hundred years 

 ago as regards the cardinal features, the recognition of a 

 geological succession in time, the origin of stratified and 

 unstratifiad rocks, the significance of fossils, and the develop- 

 ment of stratigraphy. We shall have to omit the theories of 

 the natural philosophers, the foremost of whom were Leibnitz 

 and Buffon, regarding the origin of the earth and its inhabitants, 

 suggestive as they were, and proceed at once to the results of 

 scientific research. 



According to Geikie, the distinct idea of a geological suc- 

 cession arose with Lehmann, in 1756, as the result of his obser- 

 vations in the Harz mountains and in the Erzgebirge. He class- 

 ified mountains according to age, and drew sections showing 

 the order of the strata upon their sides, and distinguished 

 between the center of older origin and the fossil-bearing strata. 

 Similar observations were made by Pallas, in Siberia, in 1772- 

 1776, and they were carried further by Fuchsel in his history 

 of the mountains of Thiiringen in 1762. He believed that strata 

 had originally been laid down in the bed of the ocean as sedi- 

 ment, and were subsequently displaced or tilted by earthquakes 

 or oscilla lions of unknown origin. He recognized that differ- 

 ent strata have their characteristic fossils, which he regarded 

 as the remains of plants and animals, an opinion by no means 

 general at that time. He inferred that the land was above the 

 sea level during the growth of the i)lants whose remaios he 

 studied. None of these three men seems to have distinguished 

 between the essentially different rocks of the mountains they 

 studied, or to have formed a theory of their origin beyond that 

 they were deposited as sediment from water. 



About 1787 there arose to prominence Abraham Gottlob 

 Werner, who, though wrong in his theory and a despot in his 

 opinions, yet by a personality of unusual power, by his system- 

 atic arrangement of data and his enthusiasm, gathered about 

 him a large following of devoted students, and ruled the world 

 of geological opinion until near the time of his death in 1817. 



Werner went back for part of his theory to Leibnitz and 

 Buffon. The two foundation principles of his doctrine were, 

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