LITHOLOGY. 1 53 



often seen to be hexagonal. Here and there in the mixture of carbon- 

 ates a kernel of aiigite is found; apatite needles are very abundant; also, 

 crystals of magnetite. Here and there a well formed crystal of horn- 

 blende is seen, and also a bit of pyrite. The chlorite that is very spar- 

 ingly present can be called nothing better than viridite, for it is in 

 minute, formless bits, which in polarized light behave like an amorphous 

 substance. 



As the feldspar is quite fresh and predominant in amount, an analysis 

 of this rock may have some value as indicating its original nature. It is 

 indeed interesting to note that with the complete destruction of the 

 augite, the feldspar has so well maintained its identity. This rock from 

 Bemis brook gave Mr. Pease, of the Sheffield Labratory, — 



Silica, 47 64 



Alumina, ............ 18.35 



Iron sesquioxide, 4.20 



Iron protoxide, 6.52 



Manganese protoxide, .16 



Lime, 7.08 



Magnesia, 4.36 



Soda, 3.31 



Potash, 1.96 



Water, 2.33 



Carbonic acid, 5.01 



100.92 



The calculations on analyses of such heterogeneous mixtures are not 

 very satisfactory, and if we allow at the highest twenty per cent, for car- 

 bonates, iron oxide, &c., the silica is increased to sixty per cent, but as 

 we know that silica that is liberated by decomposition is often present in 

 such rocks in unrecognizable form, the probability that these are labra- 

 dorite rocks is indicated. 



The variations in this variety of diabase are not wide. A specimen 

 from Tripyramid mountain contains much more unaltered augite, but 

 is otherwise the same. The Flume at Lincoln is made by the disinte- 

 gration of a diabase identical with that from Bemis brook, save that it 

 contains more iron oxide and pyrites, which aid its decomposition. A 

 dyke at Dixville is the same, but more green chlorite has been formed, 

 VOL. IV. 20 



