346 PRE-CAMBRIAN VOLCANIC BOMBS. 



investio-ation of the relation of these very distinctive varieties 

 of io-neous rocks would be desirable. 



The views respecting the formation of these bombs uhich I 

 would offer for consideration are these, that during the propul- 

 sion upwards of the erupted dust and steam, there was a rapid 

 growth of these spherical forms, augmented during flight, after 

 partial cooling had taken place, by additions received from 

 instrusions of fresher and hotter blasts meeting the descending 

 bombs ; that the agglomerates resulted from the clash of matter 

 still in the formative stage and the process of cementation was 

 very rapid and took place during the time of flight, the drying 

 of the crust being completed in many cases even before the 

 bombs fell back to earth. 



