38 Notes on the Diabase Rocks of the Buchan District. 



3. The alterations which have taken place in the two 

 groups of rocks are analogous to each other. There appears 

 to have been more or less molecular decomposition and 

 recomposition of the rock-forming minerals. The alteration 

 products of the Snowy Bluff rocks have been silica and 

 silicates, while those of the Buchan district have been silica, 

 silicates, and also carbonates. This difference is only due 

 to local conditions. 



4. If olivine be regarded as an essential constituent of 

 basalt, and as marking the distinction between that rock 

 and augite-andesite, as well as between melaphyr and 

 diabase, then this rock both of the Snowy Bluff and of 

 the Buchan district would be referred to Diabase. 



