84 Notice of Active and Extinct Volcanos. 



2. The reason of the difference in their mechanical tex- 

 ture, and the circumstances under which the trap rocks were 

 formed. 



3. The reason of their greater compactness, their stony 

 aspect being attributed to the slowness with which they 

 cooled. 



4. Why submarine lavas have cooled slowly. 



5. The character of the volcanic products, formed while 

 the ocean was retiring. 



6. The character of tertiary volcanic products. 



7. That of modern volcanic products forming streams and 

 not beds. 



8. The character of lavas, of the second class, with the 

 formation of tuffs, which the author is unwilling to attribute 

 to mud eruptions, but refers them to water, although not to 

 diluvial action. 



9. The rocks formed or ejected through the medium of 

 dykes, with the changes produced by dykes on the rocks 

 which they traverse. 



10. The difference between trap rocks and the products of 

 modern volcanos, and the cause of the columnar structure 

 common among trap rocks. 



1 1 . Arguments for and against the igneous formation of 

 granite and other rocks. 



1 2. Evidences of a central heat. 



13. Local causes of heat in mines. 



14. Final causes of volcanos, and the evidence of their ex- 

 istence from the beginning. 



It will be at once obvious, to those who are conversant 

 with geology, that each of these topics is a fruitful text, from 

 which extended and interesting discussions may be derived ; 

 those discussions, however appropriate to geological lectures 

 and treatises, would be misplaced in a Journal of Science. 



We will, therefore, close our citations and analysis, by 

 the concluding remarks of the author, to whom we have been 

 indebted for so much entertainment and instruction, and of 

 whose work we have made a free use, believing it both deco- 

 rous and useful so to do, in a country so remote from that 

 where it originated, and in which it is as yet but little known. 



"For my own part, however seductive it maybe to the imagi- 

 nation to explain on some one broad principle the phenomena of 

 our globe, and to lay down the great ends which volcanos are cal- 



