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MUSEUM OF COMPARATIVE ZOOLOGY. 



41 



was aiiskilled, or else his work was not douc with sufficient care, per- 



haps both. The line of contact is, Mlien found, a distinct separation 

 between the two rocks ; on one side of which is to be seen schist, on the 

 other " diorite." They no more pass into each other than do oil and 

 water in the same vessel, although it might not be impossible that some 

 would not be able to say where one ended and the other began. The 

 contact of the two rocks is so well marked that hand specimens (171, 

 172) can bo obtained showing it; therefore our proof that they do not 

 pass into each other, but are entirely distinct formations, can be exam- 

 ined not only in the field, but also in the cabinet, and if need be under 

 the microscope. 



Such a contact between the schist and " diorite *' can bo seen a short 

 distance east of Ishpeming, where the carriage-road, near the railroad 

 leading to Negaunee, bends around a low "diorite " knob. This junc- 

 tion is represented in plan (Fig. 18) l)y a sketch made on the spot, 

 and shown by specimens 171, 172. The "diorite " at this point appears 

 to have passed oblicpiely up through and over the schist. The relation 

 that the two have, the kind and manner of contact, are those beloiiirino- 

 to an eruptive rock breaking through and partially over another. It is 

 almost needless to say that the "diorite "is the eruptive rock here. 

 Many of the " diorite '' hills, if not all, arc composed of dikes of the 

 "diorite," with schist and argillite lying between. The lamination of 

 these interlying masses is of course generally perpendicular to the pres- 

 sure, i. e. parallel with the dikes. This can be well seen in the hills 

 south of Teal Lake, Negauuce, as well as just northeast of the Cleve- 

 land mine, IshpGming. At the latter place the "diorite " is seen to 

 break obliquely through the schist, and the line of junction can be easily 

 seen. (Fig. 19.) So far as can be told, the "diorite" comes out ob- 

 liquely over the schists connected with a narrower neck below, as shown 

 in ideal section. (Fig. 20.) This would indicate, we think, that this 

 is somewhat near the old surface of eruption. This hill was seen to be 

 made up of several "diorite" dikes, with schist held between them. 

 The contact of two of them with the schist is shown in Figures 21, 22. 



At Negauuce, on a little elevation between Main' Street and the 

 Marquette, Houghton, and Ontonagon Railroad, the " diorite " is seen 

 to break through the schist, and to send small veins into it On the 

 "diorite " ridge south of Teal Lake, the "diorite "is seen (243+, 282, 

 283) to have cut through and enclosed between it some schists and 

 argillltes. This rock is very columnar, and has the general character 

 of an eruptive mass. Its junction with the schists is well marked, and 



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