G. W. Bawes— Rocks of the ''GMoritic formation:' 123 



Stoeckel's farm) was selected for analysis. It was crystalline- 

 granular in texture ; and it would be hard to detect b)^ the eye 

 any difference between it and many kinds of doleryte which 

 are found in this region. The analysis shows that in cbemical 

 composition also it is very nearly the same. An analysis of a 

 specimen of true igneous doleryte, from the trap ridge called 

 West Rock, in New Haven, is placed beside it for comparison. 

 Metadoleryte, from St(eckel's Farm. 



Silica 50-40 50-32 50-36 51-78 



Alumina 14 43 U'Vl 14-57 14-20 



Ferric oxide --- . 2-48 2-47 2-48 3-59 



Ferrous oxide -- _ 8-28 8-35 8-31 8-25 



Manganous oxide -43 ,49 -46 "44 



Lime .. 11-15 11-11 ll-]3 10-70 



Magnesia 7-65 7-59 7-62 7-63 



Soda 3-01 3-08 3-04 2-14 



Potash -43 -44 -44 -39 



Titanic acid 1*65 1-74 1-70 



Chromic oxide ... tr. tr. tr. PgOg . . . . -14 



Ignition .. -74 -83 -78 -63 



100-65 101-13 100-89 99-89 



Specific gravity 3'04 3-03 



The close resemblance between the igneous and the meta- 

 morphic rock will be noticed ; they differ from one another less 

 than do the different varieties of doleryte. Moreover, observa- 

 tions made upon thin sections indicate that the rock is com- 

 posed of pyroxene, a triclinic feldspar, and a black opaque 

 mineral which the analysis shows to be titanic iron. The 

 pyroxene is a dark-green variety, but clear and undecom- 

 posed. If we assume that the pyroxene of this rock is of the 

 same composition as that of tlie New Haven dolerytes,* the 

 magnesia indicates that it contains 55 per cent of this ingredi- 

 ent, which being subtracted along with 3 per cent of titanic 

 iron, leaves 41 per cent of a mineral, the oxygen ratio of which 

 is very near to 1 : 3 : 6 — proof that the feldspar is labradorite. 

 Hence, the physical appearance, the chemical composition, and 

 the proportion between the mineral constituents all show a 

 very close resemblance to doleryte. The name of raetadoleryte 

 seems therefore to be particularly appropriate for this rock. 



2. Metadiahase — The chloritic variety, which has been re- 

 ferred to, resembles diabase in appearance as closely as the 

 preceding kind does doleryte. There are, however, 



in the proportion between 

 )ticed in dial 



the mineral constituents than is noticed in diabase ; for the 

 rock is sometimes uniformly crystalline, and sometimes coarsely 



