30 BULLETIN OF THE 



This relation is well shown in and about the Lake Superior mine at 

 Ishpoming. On the north side of one of the abandoned pits just east of 

 the main workings, the junction of the jasper and ore with the chlorite 

 schist was observed and figured. (Fig. 1.) Specimens were also taken that 

 show the contact (143, 144, 145, 146, and 147).* The junction of the two 

 is very irregular, the banding of the jasper and ore following the irregular- 

 ities of this line, while the schist is indurated and its lamina) bear no rela- 

 tion to the line of contact. Stringers of ore project into the schist, which 

 near the jasper is filled with octahedrons of magnetite. The schist loses 

 its green color generally, and becomes apparently an indurated argillite. 

 The contact and relations of the two rocks are not such as are seen when 

 one sedimentary rock is laid down upon another, but rather that observed 

 w'hen one rock is intrusive through another ; and in this case the intru- 

 sive one is the jasper and its associated ore. On the south side of the 

 same pit the jasper bows in and out in the schist, forming at one place 

 a projecting knob whose banding follows its contour. Lying against it 

 is a long arm of jasper, similarly banded, which ends in a rounded knob. 

 This is represented in plan (Fig. 2), and specimen No. 150 was taken 

 from the end of the latter projection. In the southwest corner of the 

 same pit a dike of very fair hematite ore (155) about one foot in 

 width breaks at an angle of 15° aci'oss the ai-gillite (154) and schist, 

 whose lamination is vertical. (Fig. 3.) Wherever the unbroken con- 

 tact of the jasper and ore with the schist could be observed, that junc- 

 tion is seen to be an eruptive one, on the part of the former (156, 157, 

 and 158). At the School-house mine east of the Lake Superior mine, 

 the jasper forms a dike with a knob-like ending, the lamination (band- 

 ing) following the curvature of the sides. The contacts between the 

 ore and schist were well-marked eruptive ones (168, 169). Overlying 

 the ore was found on one side a ferruginous and quartzose breccia and 

 conglomerate composed principall}' of the ruins of the underlying ore and 

 jasper (166, 167). A similar but finer-grained rock, mostly a quartzite, 

 forms the hanging, or better the flillen wall of the New York mine. 

 This is composed, in like manner, chiefly of the debris of the underly- 

 ing ore and jasper. Mr. Brooks's statement regarding the " quartz- 

 ite " of the Marquette district (p. 18) is undoubtedly true of this rock, 

 that when he finds the " quartzite," adjacent to it will be found all that 

 is left of the ore formation. This, however, is not what Mr. Brooks 



* The numbers enclosed in marks of parenthesis refer to specimens collected by 

 the writer, and deposited in tlie Lithologieal Collection at the Museum of Com- 

 parative Zoology. 



