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we introduce by observing that his object is to recommend a 

 greater precision in the use of terms. He says, in Natural 

 History there is a well understood scale of language, e.g. A 

 Class is divided into Orders ; an Order into Families ; a Family 

 into Genera ; and a Genus into species. But against geologists 

 he imputes, that they use their appellatives with a laxity that 

 is confusing and reprehensible. He, therefore, proposes to 

 distinguish 4 orders of subdivisions in geology, as the following, 

 placed according to their rank. 



1st. Order, called Eras. 



2nd. — „ Periods. 



3rd. — „ Epochs or Systems. 



4th. — „ Ages, Stages, or Horizons. 



1 



The Spinatus Beds e.g., would 



1. To the Mesozic Era. 



2. „ Liassic Period. 



belong to the uppermost beds ^-3. „ Middle Lias system, 

 of the Middle Lias. 4. „ Spinatus Stage, Age 



J 



or Horizon. 



The word formation should only be used to denote the mode 

 of formation e.g. The Spinatus beds are of marine formation. 



Li- the interest of the exact sciences, I have digressed to 

 introduce the topic ; and it would be well if all would strive to 

 profit by the well meant aim, to ensure greater exactitude in 

 the use of technical language. 



A few words may be admissible on the general nature of 

 Zonal subdivisions of the Jurassic or other sedimentary 

 formations, as the subject is often misrepresented. An 

 Ammonite Zone, which, by the way, begins in a practical need, 

 can only express by vague hint or symbol, the spirit or life of a 

 period. Supreme as the Ammonite may be, it credibly 

 witnesses the recognition of the life of such period. It is as it 

 were an exponent of an assemblage of life forms of limited 

 range ; and so, in truth, marks a particular phase of life, and 

 brings it into prominence, where, otherwise, it would be 

 obscured, or even passed by unheeded. This, a mere conventional 



