1076 PRINCIPLES OF STRATIGRAPHY 



(Grabau-13 ip^", pp.) Here belong, further, ancient buried cities, 

 like Pompeii ; the Roman coins, weapons, etc., buried in the peat 

 bogs of Flanders and the north of France ; and, in fact, all artificial 

 productions of early man or other animals which have been pre- 

 served. Finally, coprolites, or the characteristic excrementa of 

 animals, have frequently been preserved, and these constitute a 

 class by themselves. Thus four distinct types or classes of fossils 

 may be recognized, viz.: (Grabau and Shimer-14 :j.) 



1. Actual remains and their impressions. 



2. Tracks, trails, and burrows of organisms. 

 '3. Artificial structures. 



4. Coprolites. 



These may now be discussed more fully. 



Types of Fossils. 

 I. Actual Reiiiains. 



Preservation of Soft Tissues. As has already been noted, a 

 numl)er of cases are known where the fleshy portions of animals 

 have been preserved. The mammoth {Elcphas primigenius) , and 

 the rhinoceroses frozen into the mud and ice of Siberia are classi- 

 cal examples. Insects, spiders, and myriopods have been preserved 

 in great perfection in the Oligocenic amber of the Baltic provinces. 

 This fossil resin was produced by a species of pine (Pinus succini- 

 fer) and its quantity was so great that the deposits, though they 

 have been worked since very ancient times, have not yet been 

 exhausted. 



Remains of man and other animals have l^een found perfectly 

 preserved in peat-bogs where they had been entombed for hun- 

 dreds of years. Mummification, or the preservation of the flesh 

 in dried condition, must also be noted in this connection, for in 

 this manner many remains of the human period have been pre- 

 served. Natural mummies have been found in saline soil at Arica 

 in Chili (South America), and they have also been found occa- 

 sionally in dry caverns and in crypts, notably in Bordeaux, France. 

 In the desert region west of the Peruvian Cordillera in South 

 America climatic and other conditions have proved particularly 

 favorable to the natural preservation of human remains. "The 

 tombs and graves [of the Incas] are usually found on elevated 

 places outside of the valleys where the extreme dryness of the air 



