THE A B C OF FOSSILS. 



By Lancaster D. Burling. 



We shall start out with a definition which would 

 do if we were writing a scientific treatise but we 

 shall make every effort to break away from the 

 technical method in what follows. As the definition 

 will show, however, even the technical may be per- 

 fectly simple, and might often be more so than it is. 



Fossils are direct evidences of life preserved by 

 natural burial in the rocks of the earth's crust. 



Fossils therefore represent life and occur in rock, 

 but they need not be the actual remains of plants 

 or animals, and the rock need not be the hard sub- 

 stance which we usually think of when we hear that 

 term. In fact many beds of sand, mud, clay, and 

 marl come within our definition, and all hard rock, 

 with the exception of those that are igneous or 

 volcanic, was once soft. It has been hardened by 

 pressure, heat, and cementation (cement-ation) dur- 

 ing the ages that have passed since it was first laid 

 down. 



Although a layer of lava (molten rock) flowing 

 into water has been known to trap clams that were 

 crawling over the chilled surface of a previous layer 

 of the same kind of rock, and fossil clam-bakes of 

 this kind have been found on Vancouver Island, for 

 example, fossils are almost always confined to 

 sedimentary rock. By this we mean rock which 

 has been formed from wind-blown dust or sand; 

 from the mud, sand, or gravel in river beds or val- 

 leys; from the sediment which falls to the bottom 

 of ponds, lakes, or oceans; from the material piled 

 up or carried by ice rivers, or glaciers; and from 

 deposits for which animals and plants are responsi- 

 ble, for example coral reefs and coal beds. It will 

 easily be seen that sand or mud settling in water 

 would arrange itself in comparatively flat layers, but 

 all sedimentary rocks, whether thrown together by 

 the wind, by a river, by the waves, or by a glacier 

 are piled up in similar layers; they are stratified to 

 use the proper term, and this stratification is often 

 surprisingly regular. 



The amount of mud and sand which is being 

 carried by rivers into the ocean, where it must of 

 course all settle, has been computed for the 

 Mississippi, but instead of giving you the number 

 of billion cubic feet a year or the number of hun- 

 dred million tons a year let us suppose that someone 

 should put in the plant needed to strain this mud 

 and fine sand out of the water before it reaches New 

 Orleans and should send it past that city in canal 

 barges. If these barges were 100 feet long the 

 people in New Orleans would see a barge full of 



sand pass every 10 seconds or less, and since it would 

 take the river 30 seconds to float a 100 foot barge 

 past a given point the barges would have to pass in 

 bunches of three and there could be no space be- 

 tween the back of one set of three barges and the 

 front of the next. If the man we have imagined 

 were to take care of all of the sand and mud for a 

 year he would have to work day and night, Sundays 

 and holidays, winter and summer, and never allow 

 an inch of space between each set of three barges. 

 If these were to dump their loads in the Gulf of 

 Mexico the sand would settle in piles but the river 

 spreads it out very widely and sends enough material 

 each and every year to spread a one inch carpet over 

 more than 3000 square miles of the gulf's bottom. 



This gradual piling-up process, one which takes 

 place on land as well as in the water, affords a con- 

 tinual opportunity for the natural burial of the re- 

 mains of the animals or plants that die and drop to 

 the bottom. Those remains that do not decay and 

 are preserved, however this may be done, are called 

 fossils. So also are the casts or molds of animals 

 that do decay, their footprints, etc. Whatever the 

 form of the evidence that the animal or plant once 

 lived, it simply must be direct, and whatever the 

 manner in which the burial took place, it must have 

 been by natural means. For example, hard coal, 

 though we know it to be formed of plant remains, is 

 not a fossil, the evidence is indirect ; and a dog does 

 not make a fossil, or even start one on the way, when 

 he buries a bone. The latter may be a perfectly 

 natural thing for the dog to do but it does not come 

 within our definition of the term natural, a fact 

 which will be perfectly clear before we are through. 



An animal tries to cross a slough and gets mired, 

 or sinks in quicksand, another breaks through the 

 hardened surface of a tar pool and disappears, a 

 jelly-fish is stranded on a tidal flat and the next tide 

 covers it with a layer of sand or mud, an animal 

 walks across some drying mud and the next rain 

 washes sand into its footprints, an insect gets caught 

 in a drop of resin, a mammoth is frozen in the ice 

 in a polar climate, an animal dies on the desert and 

 its whitened bones are covered by the next sand 

 storm, a leaf sinks to the bottom of a pool and is 

 covered with mud, a snail or a clam dies and the 

 shell lies on the bottom of the ocean until it is 

 covered, a coral or a sponge growing on the bottom 

 is smothered by a shifting of the current which 

 covers it with sand. 



