Handbook of Paleontology 185 



same name though lithologically different. Sometimes 

 further study, particularly of the fauna, shows that a 

 thick succession of like sediments, such as shales or lime- 

 stone beds, which have always been regarded as a single 

 lithological unit, is made up of several distinct members 

 to which formation names are given. The old name may 

 be discarded or used to designate a part of the previous 

 compound formation. 



William Smith (1769-1839), known as "Strata" 

 Smith and the "'Father of English Geology and Strati- 

 graphy" was the first to recognize the value of fossils 

 in determining the age of formations, (1799-1801). 

 English geologists have played a leading part in the 

 detailed subdivision of the rocks of the earth's crust 

 and therefore we find that many of the terms that have 

 in general a world-wide acceptance were proposed by 

 them. Much has been done since then in countries 

 all over the world. Divisions have been more exactly 

 delimited and with closer study finer and finer sub- 

 divisions have been made. Fossils now are regarded 

 as the primary basis for determining the sequence of 

 geological formations, and when they are not present 

 age is determined by a study of the lithological char- 

 acter and other considerations. There are many things 

 that make the correlation of formations difficult. Fold- 

 ing and faulting may have disturbed the normal se- 

 quence or again through erosion isolated patches, 

 separated by great distances, may be all that remains 

 of a bed of rock. The lithological character of a rock, 

 also, may change from one place to another, or forma- 

 tions may be separated by an unconformity, the miss- 

 ing beds being present in another locality. By study- 



