10 EDWIN GILPIN ON THE 



miles, contains sevoral beds of limestoue, which apparently underlie the gypsnm, and may 

 be called manganiferons. These measures carrying manganese re-appear again south of 

 "Windsor, and at Douglas, fifteen miles south of Teuuy Cape, near the line of their 

 junction with the pre-carboniferous rocks. In this range of measures the manganese of 

 Tenny Cape appears to be principally connected with a compact red and gray limestone, 

 which, fi-om the analysis already given, may be called a dolomite. At the western end of 

 the district it occurs as veins in conglomerates and sandstones, and also in limestones 

 in places decidedly magnesian. 



The Tenny Cape manganese ores were discovered about the year 18G2, and haA-e been 

 intermittently worked since that date. The limestone baud to which they seem to be 

 principally confined is about 300 feet thick. The ore occurs in irregular nests, and in 

 seams eroded on the bedding-planes and cross-fractitres. It thus occurs that large 

 masses almost entirely isolated have been met, also seams with occasional pockets, some- 

 times connected, but in no case, so far as I am aware, following any regular order of 

 position or extent. The largest mass yet found was estimated to contain 180 tons of ore. 

 Apparently, the ore has been deposited at irregular intervals of time, with the associated 

 minerals, in the openings worn by the action of water on the limestones. Specimens may 

 be obtained showing pyrolusite, cementing waterworn pieces of limestone, and surround- 

 ing nodules of the bed-rock which haA^e resisted erosion. The ore is chiefly a fibrous 

 pyrolusite, with splendent lustre, based on a compact or granular ore consisting of pyro- 

 lusite, of psilomelane, and of manganite, the latter mineral however not being present in 

 large q^^antity. The quality of these ores, even after the slight hand-dressing they receive 

 at the mines, is very high, and in some years they bring .$125.00 a ton at the mine. They 

 are prized by glass-makers for their freedom from impixrities, especially of iron. This 

 high grade of the pyrolusite from the Tenny Cape district will appear when, from 

 numerous assays, it has been found to yield from eighty-eight to ninety-five per cent, of 

 EA^ailable oxide. The following analyses show the general character of these ores : — 



Douglas. ' Cheverie. ' 



Moisture 1-660 2-05 



Water of composition 3-630 — 



Iron peroxide -603 2-55 



Oxygen 7.035 — 



Baryta 



Insoluble matter 



Phosphoric acid 



Manganese oxides S4 -620 



Peroxide of manganese 



Lime 



100-000 99-699 



At "Walton and Cheverie manganite is more common than at Tenny Cape. Its mode 

 of occurrence is similar, and its general character is shown by the following analyses : — 



' Contains some psilomelane ; analyst, H. Poole. 

 2 E. Gilpin. 



