4 AN INTRODUCTION TO THE STUDY OF FOSSILS 



beasts occur in caves of western Europe preserved by such a 

 stalagmite covering. 



During a time of increasing cold, as at the beginning of the 

 late Glacial Period, the bogs within the colder areas became 

 frozen. In these natural refrigerators remains of plants and 

 animals are well preserved. 



As resin stickily exudes from trees it is apt to hold all small 

 objects that touch it, especially seeds and insects, and these are 

 soon completely inclosed by it. Fossil resin, known as amber, 

 is found in various parts of the world, but is most abundant in 

 the Oligocene beds along the Prussian shores of the Baltic Sea. 



The water of peat bogs and marshes has antiseptic properties, 

 and because of this organisms immersed in it decay very slowly. 

 Logs long inclosed in such waters have been dug up and utilized 

 in various regions, such as southern New Jersey. 



Volcanic eruptions are at times accompanied by very much 

 fragmental material, especially ash. This ash, falling thickly, 

 is apt to bear down with it many insects, and if falling into a 

 shallow lake, will bury them with such other organisms as may 

 be there present. Such showers occurred at times during the 

 Miocene at Florissant in Colorado, and to them we doubtless 

 owe much of the marvelous record of insect life there preserved 



(Fig. 137)- 



Similarly, when prevailing winds blow from a dry into a moist 

 region, or from an area without vegetation to one with it, dust 

 will accumulate in the latter region, resulting in time in thick 

 deposits of unconsolidated, fine, porous, siliceous silt. Such 

 deposits, called loess, are especially abundant in North America, 

 Europe and Asia, from Pleistocene times to the present, and are 

 apt to contain land shells. Some loess is of aqueous origin. 

 The coarser wdnd deposits, such as sand dunes, are not likely 

 to contain fossils ; such an unfossiliferous dune deposit is seen 

 in the coarse-grained, white sandstone of Jurassic age in southern 

 Utah. 



The vast majority of organic remains preserved as fossils 



