BY E. D. PETERS, JUN., M.E., M.D. 195 
the bog, you will find fresh bright crystals or nodules of iron pyrites. 
Select a blade of grassor stem of a plant that bas a little bunch of these 
crystals hanging to it, and after counting them and drawing an exact. 
sketch of them in your notebook, return in a month and investigate 
again. If the conditions are favourable, you will not only find many new 
crystals, but a great augmentation in size of the original ones. This is 
without question the key to the formation of Mount Lyell and all 
similar pyrites deposits, and it is almost universally accepted as such by 
thoze who have given the subject attention. I myself feel no doubt in 
the matter. Organic, peaty acids have this power of reducing soluble 
sulphates of certain metals to insoluble sulphides, and precipitating 
them in situ. if it is done very slowly, the metals will be thrown 
down in a more or less crystalline form. If rapidly, in an amorphous 
and massive form. The subsidence of the land, and the consequent 
filling up of the ponds with sulphides, continued through many hundreds 
or thousands of centuries. But at last camea time when the elevation 
of a ridge, or some change in the configuration of the country, the 
supply of metallic waters was cut off from our pond-holes, or, more 
probably, lost in the inundation of muddy waters that blanketed all 
this region with a thick layer of hydro-mica-schist, and the sulphides 
disappeared from view, to undergo, under its heavy covering of mud 
rocks, the changes and metamorphoses that time and heat are sure to 
bring about. Successive layers of pebbles, of sand and of other debris 
buried our hydro-mica belt, till at last came the final act in the great 
drama, and the stage was set for the last act, the period which we now 
see. This last shifting was, perhaps, the most striking and dramatic of 
any of the various scenes that I have endeavoured to portray, and 
furnishes us with many interesting and obvious details, that if I could 
only dwell upon would tend greatly to prove the correctness of the 
theory here advanced, as well as to explain many interesting, and 
apparently difficult, details that we now notice in the deposit, This 
was the last period of mountain building, in which the present great 
elevations were reared, and the strata between them were dislocated 
and set on edge. Wherever a break happened to come across one of our 
bog-hole deposits of sulphides we are enabled to find and utilise them. 
But the chances are infinitely against such a piece of good fortune, and 
no doubt dozens of such pyrites masses are buried unsuspected under 
the rocks that we daily walk over in the vicinity of Lyell, some of them 
hundreds of thousands of feet from daylight, and others, quite possibly, 
within a few feet of our unsuspicious boot soles. I can only compare it 
to a flat cake, containing a very few plums scattered through its interior. 
Let us break this cake across in two or three places, and set the frag- 
ments up on edge ina plate. Out of the dozen or more plums that our 
supposititious cake may contain, we may, perhaps, bring one or two to 
light, and in the same way nature and accident have opened to us such 
deposits as those under consideration. Mary other deposits, equally 
good or better, may exist in close proximity to the single one or two 
that happen to be brought to the surface by the breaking and tilting of 
the strata, but nothing betrays their presence, and unless we find them 
by deep boring, or by running prospecting tunnels at a ventare, their 
wealth will remain wasted to us. Let us assume, therefore, that the 
strata have been broken across in such a manuer that the line of fracture 
comes across one end of our bog-hole, now filled with pyrites, and 
deeply covered by other strata of rocks. Let us further assume that 
the fractured strata are next tilted so that the exposed end of the 
sulphide body comes to the surface, and the whole mass of pyrites, 
instead of lying in its original horizontal position, is now standing on 
edge, so that what was originally its depth is now its thickness, and 
what was once its lateral extent is now its depth. This is the present 
condition of the Mount Lyell mine, and, bearing this in mind, it is 
