hill] A LESSON ON FOSSILS 395 



In preparation the clay is placed in a pan or bucket or large jar 

 and covered with a very wet cloth for twenty-four hours. Do not 

 wring the water out of the cloth and do not put the clay in water. 

 To make impression fossils, flatten out the piece of clay, making 

 it about half an inch thick. Smooth off the top with the knife 

 or wooden stick. This makes the surface of the clay smooth, like 

 the surface of a mud flat by the sea, where shell fossils are made 

 or near rivers where leaves fall or drift in and remain. Lay the 

 leaves on the surface of the clay with the under side of the leaf 

 next the clay (the under surface of the leaf makes a better impres- 

 sion than the upper, because the veins stand out more). Press 

 upon it hard with the hand, or better with a piece of glass or board. 

 Let the leaves remain on the clay and put away to dry. Of course 

 in real fossils the leaf remains and traces of its substance may 

 sometimes be detected with the impression. 



In making shell impressions choose shells which have grooves 

 or ridges in order that the impressions may not be smooth and 

 characterless. Press the shell into the- clay and then gently pry 

 it out, unless it is a flat shell, or unless it is desired to represent 

 the imbedded fossil which is a little less like the real because it is 

 white. These clay fossils should also be put away to dry. If 

 trilobite fossils are at hand compare with the pillbug, showing 

 the segmented back, but noting the three areas on the trilobite 

 and only one on the pillbug. A crayfish or lobster, though so 

 much larger, will show the marks of relationship. If one of the 

 trilobites is in a curled up position, by touching the pillbug it can 

 be made to curl up in the same position which gave it its name, 

 I suppose. Both trilobite and pillbug are crustaceans, relatives 

 of the lobster, crayfish, shrimp and crab. 



What a Fossil is 



If we walk along the seashore and dig in the sand we find shells 

 and remains of sea animals, that have been buried by sand, brought 

 by the waves and high on the beach, drifted over by the winds. 

 On a mud flat we find leaves, sticks and logs brought down by the 

 river and deep in the mud, clams, worms and other animals, layer 

 after layer of mud may cover them. If the beach and mud flat 

 were to be raised and made into rock as earth forces have done in 

 the past, these shells, leaves, etc., would become fossils. 



