FOSSILS, AND HOW THEY ARE FORMED 5 



gently as dew upon the grass. Little by little the bones 

 are covered by a deposit that fills every groove and pore, 

 preserving the mark of every ridge and furrow; and 

 while this may take long, it is merely a matter of time 

 and favorable circumstance to bury the bones as deeply 

 as one might wish. Scarce a reader of these lines but 

 at some time has cast anchor in some quiet pond and 

 pulled it up, thickly covered with sticky mud, whose 

 existence would hardly be suspected from the sparkling 

 waters and pebbly shores. If, instead of a lake, our 

 animal had gone to the bottom of some estuary into 

 which poured a river turbid with mud, the process of 

 entombment would have been still more rapid, while, 

 had the creature been engulfed in quicksand, it would 

 have been the quickest method of all; and just such acci- 

 dents did take place in the early days of the earth as 

 well as now. At least two examples of the great Dino- 

 saur Trachodon have been found with the bones all 

 in place, the thigh bones still in their sockets and the 

 ossified tendons running along the backbone as they 

 did in life. This would hardly have happened had not 

 the body been surrounded and supported so that every 

 part was held in place and not crushed, and it is diffi- 

 cult to see any better agency for this than burial in 

 quicksand. 



If such an event as we have been supposing took 

 place in a part of the globe where the land was gradu- 

 ally sinking and the crust of the earth is ever rising 

 and falling the mud and sand would keep on accumu- 

 llating until an enormously thick layer was formed. The 

 cime or silica contained in the water would tend to 

 sement the particles of mud and grains of sand into a 

 polid mass, while the process would be aided by the 

 tressure of the overlying sediment, the heat created by 

 h \s pressure, and that derived from the earth beneath. 



