QUESTIONS. 341 



185. What is said of the thickness of the Azoic strata ? What of 

 the upheavals and flexures of them ? What of the rocks of this age ? 

 What of the temperature of the forming crust ? 



186. Give Hugh Miller's description of the commotions attending 

 its formation. 



187. Why could not life exist in this age ? What was the condition 

 of the surface of the land at the end of it ? 



CHAPTER XIV. 



187. Why is it inferred that life was introduced at the beginning 

 of the Silurian age ? 



188. Why is it supposed by some that life was introduced before 

 this? What reason have we for saying that life was created? What 

 is said of species ? What are the rocks of this age ? What is said of 

 the rocks at Niagara Falls ? 



189. Why is this called the Silurian age? What is the arrange- 

 ment of the Silurian system in New York ? 



190. What is the geographical distribution of the Silurian rocks, so 

 far as ascertained ? State the origin of the copper of Lake Superior. 

 What is said of the salt springs in this country ? 



191. State Dana's way of accounting for the great accumulation 

 of salt in the State of New-York. Trace the comparison in regard 

 to the lagoon. How is the salt obtained from the springs in New- 

 York? 



192. How was the gypsum, which abounds in the Silurian forma- 

 tion in New York, produced ? Where gypsum and salt are found to- 

 gether, how are they separated ? State in full what is said of "the 

 Silurian beach." 



193. What is said of the traces left by water? State in full what 

 is said of life in the Silurian age. 



194. What was the condition of the atmosphere in this age ? Show 

 how the animal world was adapted to it. Give what Agassiz says of 

 this adaptation. What was the source of the carbonaceous matter in 

 the Silurian shales? 



195. What are the Hydrozoa and Bryozoa of this age? What is 

 said of the corals and echinoderms ? 



196. What of the chain coral ? What of the crinoids ? 



197. Name the three classes of Mollusks, and state what is said of 

 each. 



198. What are the Brachiopods, and what is said of them ? What 

 is said of the Lingula? Of the Orthoceras? What of the Cephalo- 

 poda in this age, in contrast with the present ? 



199. What is said of the Trilobites? 



