10 ILLUSTRATIONS. 



Plate XXIX. A, Basalt showing characteristic texture in ordinary light ; B, Basalt showing 



obliteration of texture hetween crossed nicols 288 



XXX. -1, Basalt showing in ordinary light a distinctly amygdaloidal texture; B, The 

 same basalt with its amygdaloidal texture obliterated when viewed between 



crossed nicols 290 



XXXI. A, Ba8;iJt affected by calciflcatiou process; B, Basalt affected by calcification 



process viewed between crossed nicols 292 



XXXII. A, Illustration of perlitic parting in a fragment from a basaltic tuff; B, Sickle- 

 shaped bodies in volcanic tuff 294 



XXXIII. A, Water-deposited sand; B, Gradation in water-deposited volcanic sediment . .. 296 



XXXIV. J, Contact product of granite; 5, Brecciated matrix between ellipsoids 298 



XXXV. A, Contact between granite and a metamorphosed sedimentary; B, Contact 



between granite and a metamorphosed sedimentary viewed between crossed 



nicols 300 



XXXVI. A, A variety of spilosite with white spots; B, A variety of spilosite with white 



spots viewed between crossed nicols 302 



XXXVII. A, Normal spilosite or spotted contact product ; B, Normal spilosite of some- 

 what different character 304 



XXXVIII. A, Passage of spilosite into demosite; B, Occurrence and alteration of bronzito 



in l)ronzite-norite 306 



XXXIX. A, Biotite-granite viewed between crossed nicols ; B, Mica-diorite viewed between 



crossed nicols 308 



XL. A, Quartz-mica-diorite-porphyry ; B, Quartz-mica-diorite-porphyry viewed be- 

 tween crossed nicols 310 



XLI. ^, Porphyritic poikilitio hornblende gabbro ; B, Poikilitic hornblende gabbro.. . 312 

 XLII. A, Moderately fine-grained hornblende gabbro showing parallel texture ; B, Mod- 

 erately fine-grained hornblende gabbro showing parallel texture viewed 



between crossed nicols 314 



XLIII. A, Normal granular hornblende gabbro ; B, Schistose hornblende gabbro viewed 



between crossed nicols 316 



XLIV. J, Moderately fine-grained hornblende gabbro; i?, bronzite-norite 318 



XLV. J, Bronzite-norite-porphyry; 5, Feldspathic wehrlite 320 



XLVI. ^, Feldsjiathicwehrlite viewed between crossed nicols; jB, Feldspathic wehrlite.. 322 



Fig. 1. Reproduction of a portion of the geological map of the Upper Peninsula of Michigan, 



by William A. Burt, 1846 15 



2. Enlarged reproduction of a portion of a map of the Lake Superior land district, by 



Foster and Whitney 17 



3. Enlarged reproduction of a portion of a geological map of the Upper Peninsula of Michi- 



gan, by Rominger, Brooks, and Pumpelly, 1873 18 



4. Granite-porphyry with inclusions of gneissoid granite 45 



5. Illustration of the effect on the topography of the differential erosion of basic dikes and 



granite 46 



6. Concentric cracks formed by the caving in of the Mansfield mine 65 



7. Sketch of the surface of the outcrop of an ellipsoidal basalt, showing the general char- 



acter of the ellipsoids and matrix 112 



8. Sketch showing the concentration of the amygdaloidal cavities on one side of an ellip- 



soid, this side probably representing the side nearest the surface of the flow 113 



9. Ellipsoids with sets of parallel lines cutting each other at an angle 114 



10. Reproduction of illustration of aa lava, after Dana 120 



11. Profile section illustrating results of diamond-drill woi'k 177 



12. Sketch illustrating contortion of Upper Huronian strata 179 



13. Sketch showing change of strike of Upper Huronian beds, due to the folds 179 



14. Sketch to illustrate the occurrence of ore bodies 182 



