72 OUR PHYSICAL WORLD 



fidelity all the details of structure. Sandstones and shales also 

 contain such fossils (Fig. 31). 



FIG. 31. A group of fossils: (a), (6), (d), (/), fern fronds; (c), an equisetum; 

 (e), an animal, a shrimp; (g), bark of Sigillaria. 



