36 



BULLETIN OF THE 



is now. The ore at tlie New Washington mine is magnetite, and it was 

 seen in distinct well-marked dikes, as unmistakable as any dike, break- 



r 



ing obliquely up through and across the argillaceous schist, No. 340 

 showing the contact of the two. These dikes were sometimes narrow, 

 being only about one foot wide, with well-marked junctions with the 

 schist on both sides. The ore is more strongly magnetic and afTeeted in 

 its character adjacent to the dikes that later cut through it than in 

 other portions of its mass (p. 43). The dikes of magnetite, with the 

 other dikes, have greatly affected the schist through which they pass, 

 forming an ottrelite schist (p. 45). At the Champion mine the ore 

 is both magnetite (35G) and hematite (355), and both are frequently 

 found in a single hand specimen (357, 358, 359). At the Keystone 

 mine, east of the Champion, a dike of magnetite about six inches in 

 width was observed. 



The Basic intrusive Rocks, Schists, and Pelsito. 



At Marquette, south of, but near, the lighthouse, a dike (3) of about 

 seventeen feet in width cuts across the schist (1, 2, 5,), the latter dip- 

 ping north seventy degrees. The contact of the dike with the schist 

 is a well-marked intrusive one, the schist being indurated at the point 

 of coi>tact (4). (Fig. IG.) .Microscopically, the rock of this dike (3) is 

 composed of phigioclaye, some orthoclase, quartz, hornblende, biotite, 

 viridite, magnetite, l^eraatite, and some probable pscudomorphs after 

 olivine. The feldspar contains nvmierous microlites and inclusions, and 

 it appears'to be the only original constituent of the rock left in a deter- 

 minable condition, except the magnetite. The schist (2) is composed 

 of a fine-grained groundmass of aggregately polarizing quartz, liolding 

 greenish ragged hornblende crystals and grains of magnetite. 



Many dikes occur in this vicinity, and their intrusive character has 

 been noticed by Credner, Eominger, and .Tulien. Some dikes (8) were 

 seen running north and south, cutting the east and west ones. The 

 relation of one of the latter to the adjacent schists is shown in Figiu'e 

 14. In the quarries near the light-house numerous dikes were seen. 

 Their lines of junction with the schists (47) could readily be made 

 out, and hand specimens obtained showing it (45, 4G, and 48). (Fig. 

 15.) Four of these dikes were counted within a distance of two hun- 

 dred and thirty-two feet, one of which was sixty-six feet in width (49). 

 The locality m the place from which the stone for the Marquette 

 breakwater was obtained. These dikes, like the majority running east 

 and west, nearly, but not quite, coincide with the bedding (45, 4G, 47, 



