220 THE JOURNAL OF GEOLOG Y. 
It is evident that in the region described the Archean forma- 
tion consists of rocks of widely different composition, and that the 
variations are frequently repeated throughout the area. 
The use of the term granite in a general sense for granular rocks, 
without regard to their composition, must naturally preclude its use in 
the narrower petrographical sense. ‘The need of some widely applica- 
ble terms to designate groups of rocks resembling one another in out- 
ward, megascopical appearance is becoming more and more urgent as 
the refinements of advanced petrography tend to discriminate more 
closely upon a basis of characters not distinguishable in the outward 
appearance of rocks. ‘The necessity of maintaining terms which may 
be applied to rocks by those not conversant with petrographical meth- 
ods of investigation, or which may be used until the precise character 
of the rock has been discovered, must be evident to all geologists. 
The same term, however, should not be used ina general and ina 
restricted sense. As others have pointed out, gvanzfe may properly be 
employed as a general term for all phanerocrystalline, evenly granular 
rocks. A new term would be required for such rocks, when composed 
of quartz, alkali-feldspars with or without ferro-magnesian silicates. 
The petrographical study of the members of the Penokee series has 
led to the conclusion that the chert and limestone of the cherty limestone 
member are water-deposited sediments, whose origin is not improbably 
organic, the silica having been rearranged and the limestone dolomi- 
tized. The study of the quartz-slate member shows its.composition 
to be varied ; that it is always fragmental, and that its induration is due 
to the secondary enlargement of quartz fragments, rarely of feldspar 
fragments. It is also due to the alteration of the feldspar to biotite, 
chlorite and quartz by the accession of material from neighboring 
sources. The source of the original fragments composing this forma- 
tion was chiefly the Southern Complex. 
The petrographical study of the Iron-bearing member has demon- 
strated satisfactorily the origin: and mode of formation of the ore- 
bodies, the substance of which is reviewed more particularly by Profes- 
sor Penrose. 
‘he upper slate member was found to be of fragmental origin, and 
was derived from the Southern Complex. Metasomatic changes have 
altered the original deposits to a greater or less extent; the extreme 
metamorphism resulting in rocks in no way distinguishable from crys- 
talline schists. This change has been most complete in nearly pure 
