107 
slaty. It generally forms a good hone stone. The skill with 
which the mound-builders have pierced and worked this hard 
and tough stone is remarkable. Among the most characteristic 
specimens of whetslate in the Blackmore Museum we may name 
the following : — Case A 48, No. 35 ; Case A 49, No. i ; No. 9 ; 
No. II, which, shows fracture; No. 27, which shows stratifica- 
tion ; Case A 50, No. 3. A further remark should be made as 
to one specimen in the Collection, Case C 35, No. 10, which 
shows the junction of whetslate with a peculiar felspathic stone 
which has been described as greenstone ash, and is distinctly 
porphyritic in texture. The Cornish killas now and then passes, 
just in the same manner, into a porphyritic rock. 
23. Argillaceous Ironstone. 
This stone, like the whetslate above described, is not a definite 
mineral, but a mixture of minerals — a rock. Its hardness varies 
in different parts of the same specimen — the harder parts 
approaching 6, and the softer parts not exceeding 4*5. These 
softer parts are paler in colour, contain much less iron than the 
harder parts, and seem to consist of minute globules of a com- 
pound silicate, perhaps a felspar. Some of the pipes and other 
objects fashioned from this ferruginous stone are much fissured 
internally, and blacker inside than out. When most compact, 
this stone has the density 4-3 ; when least so, about 3*07. In 
the following analysis the silica was ascertained "by difi"erence," 
and includes a little alkali. In 100 parts there are: — 
Silica 
. 46-42 
Ferric oxide (peroxide of iron) 
• 34'8o 
Alumina .... 
. i6'45 
Magnesia .... 
. -46 
Lime ..... 
1-48 
Water ..... 
•39 
lOO'OO 
The Collection contains many examples of this curious clay 
ironstone. Some of these approach in structure to the red 
pipestone (Coteau des Prairies), often termed Catlinite. But 
they are more variolitic in texture, and much more mottled and 
diversified in colour. Some specimens are iron grey or dark 
brown; others pale grey, spotted with white. Case A 50, Nos, 
