G. W. Hawes on Diabantite in amygdaloidal Trap. 455 
various minerals, among which the most common are carbonate 
of lime, silica and chlorite; the two former substances being 
naturally produced in the change of the bisilicate, pyroxene, to 
the unisilicate, chlorite. At one point in the Farmington hills 
these amygdaloidal cavities are of very large size, often larger 
than an egg, and in them, with the quartz and calcite, there 
are large hones masses of siderite possessing a foliated and 
radiated structure and a dark green color. This association of 
minerals, which has often been gate senystior te seemed to 
indicate that this was the chlorite which s distributed 
through the diabase, and an pay was théréfors made to 
determine to which member of the chlorite group it belonged. 
A thin section of one of the masses under the microscope 
appeared to be perfectly homogeneous, and exhibited a very 
marked and beautiful dichroism. From a cavity in which the 
chlorite had thus been shown to be pure, the material was care- 
fully selected for analysis. Its specific gravity was found to be 
2°79; its hardness, 1; and its fusibility 8. The composition 
obtained was as follows 
i ii. Mean. Oxygen 
Silica. ic cio ees 83°25 33°24 17°73 17°73 
Alumifisys: sca 11°13 Hee Ae 5°16 5°83 
Ferric oxide, -_-. - Fee 215 2°26 67 ‘ 
Ferrous oxide, . ---25°09 25°12 25°11 5°58 
Manganous oxide,. ‘40 “42 “41 
LAR) ein! Sseueetews 1:07 1°15 111 32 12°66 
MRPUOM His a 16°48 16°54 16°51 6 
ni ith tM SO Sa ieee et 25 “25 25 07 
Water, minarets hae 9°89 9°93 9°91 8°81 8°81 
99°91 99°83 99°87 
This analysis gives for the oxygen ratio of the inbigpoigi 
sesquioxides, silica and water, 4.3: : 8, showing that it 2 
proaches very closely to a unisilicate in its composition. In 
order to ascertain whether this composition remains constant, 
the analysis was repeated upon another sample selected with 
ie care from another ee a the following were the results: 
5; IL. Mean. Oxygen. 
Silica, wun 89O6.. < 89770 $868 17°96 17°96 
lumina, 10°98 10°75 10°84 5°05 t 590 
‘erric oxide, ._..-- 2°95 Ha 2°86 
Ferrous oxide, _.-.24°24 24°43 24°33 5°40 
nganous oxide,. °38 38 38 09 
Eee cis "712 “73 : “21 12°39 
Magnesia... 2. 325. 16°56 16°48 16°52 6°61 
Sos ia ee 33 33 08 
Water, See ae 10°04 10°01 10°02 8°89 8°89 
