572 



SCIENTIFIC RECREATIONS. 



Fragmental (or the " Plutonic" and "Volcanic"), including basalts, pitchstones, 

 pumice, trachytes, granite, syenite, etc.; and, on the other hand, tuff and 

 " volcanic " breccia, with felstones, porphyries, etc., which have been classed as 

 intermediary.' 



Of these three classes of rocks, the sedimentary and the organic 

 compose the greater portion of the earth. We will now glance at the crust 

 of the earth and its various formations. 



V olcanic eruption 



