PREFACE. 



A general knowledge of Geology is probably of greater importance 

 to the people of the United States than a like amount of information in 

 any other department of natural science ; but every one will admit the 

 state of learning in this branch is not of a very high grade. There is a 

 common complaint among well-informed people who have given Geology 

 no special study that the language used is technical, the names long, 

 difficult to understand, and not unfrequently bear upon their face the 

 evidence of affectation, as if those coining the words had attempted to 

 make them as obscure as possible. It is a fact, however, that technical 

 names are absolutely essential to a correct understanding of every branch 

 of Natural History; and when the system of nomenclature is once learned 

 the names are readily understood, and much more easily remembered, 

 than the arbitrary names of individual things possibly can be. In this 

 work an effort has been made to popularize the rules of nomenclature, and 

 to define the technical words in the text or in the Glossary. 



Generic and specific names, which have been used by authors where 

 the fossils are not known to occur in the Palaeozoic rocks of North America, 

 are printed in italics. Synonyms, names not described as required by the 

 rules of nomenclature, preoccupied names, and those condemned for any 

 other reason, are also printed in italics. When an author has referred his 

 species to a genus to which it does not belong, the specific name will be 

 found in italics under such generic name, and referred to the genus to 

 which it belongs, and at the latter place the original erroneous generic 

 reference will be found in parenthesis. 



An attempt has been made to define all genera known from the 

 Palaeozoic rocks of North America ; the name of the author of each genus 

 is given, the date of coining the word, and an abbreviated reference to the 

 book and page where published, and the etymology of the word and name 

 of the type species. The names of all the species, arranged in alphabetical 

 order, will be found under the genera to which they belong; and also the 

 authors of them, the dates and places of publication, and very frequently 



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