780 A. P. COLEMAN 
In addition to the comparatively large masses of eruptive rock 
thus far mentioned, there are later dike-rocks penetrating them all 
impartially, including large dikes of very fresh olivine diabase, which 
cross norite, ore bodies, granite, and different kinds of Huronian 
rocks; and a few small dikes of still later granite which cut the olivine 
diabase, and are therefore the latest rock in the district except the 
widespread pleistocene beds of clay, sand, and gravel. 
The dike-rocks are separated from the older eruptives by a very 
long interval of time, and may have no connection with the original 
nickel-bearing magma. 
TIME RELATIONS AND CONCLUSIONS 
The oldest rocks of the Sudbury district are mainly sedimentary, 
including small patches of green schist and banded silica of the Iron 
formation, belonging to the Keewatin; quartzite, graywacke, and 
slate of the Lower Huronian, associated with certain schists and 
greenstones; and Middle Huronian graywacke conglomerate in a 
small area north of Ramsay Lake. 
The granite and gneiss mapped as Laurentian penetrate the 
sedimentary rocks of the Lower Huronian, and so are later in age; 
but their relation to the Middle Huronian is not known. The basic. 
norite underlying the main nickel range may be later than the Laur- 
entian, though this is not certain, since the two rocks have not been 
found in contact. It is later than the Lower Huronian, since it 
incloses blocks of graywacke and quartzite. 
Upon the planed-down edges of these older rocks after a great 
lapse of time the Trout Lake conglomerate was deposited, followed 
by the eruption of ash and lapilli forming the thick sheet of the Onap- 
ing tuff. Next came the quiet deposit of mud forming the Onwatin 
slate, and of sand, forming the Chelmsford sandstone. 
The age of this series of rocks is uncertain, but they have been 
looked on as probably the equivalents of the western Animikie, now 
classed as Upper Huronian. Accepting this classification, the sedi- 
mentary rocks range from the top of the Keewatin, the oldest known 
formation, to the Upper Huronian or Animikie. Next came the 
flood of nickel-bearing magma spreading as a sheet a mile and a 
quarter thick between the Trout Lake conglomerate and the lower 
