NOTES. 441 
NOL EF) «6. 
(Page 109.) 
COMPOSITION OF QUARTZ-PORPHYRY OF THE GREAT PALISADES. 
Specimen 876, representing the quartz-porphyry of the Great Palisades of the 
Minnesota coast of Lake Superior contains 71.10 per cent. of silica. 
NVOLLD Ey 7: 
(Page 110.) 
QUARTZ-PORPHYRY OF BAPTISM RIVER POINT. 
Specimen 902 has 73.87 per cent. of silica. 
NOTE 18. 
(Page 152.) 
ERUPTIVE MATERIAL IN THE UPPER DIVISION OF THE KEWEENAW SERIES. 
A slight exception to the general absence of eruptive material from the Upper 
Division of the Keweenaw Series is found in the olivine-diabase dike described on page 
223, A small exposure of diabase was also noted among the sandstones of the Upper 
Division on the Saint Croix River in Sec. 35, T. 44, R. 13 W., Wisconsin, by the late 
Moses Strong (see Geol. of Wis., p. 424). It is not evident whether this exposure repre- 
sents a thin intercalated seam or a dike. Both these occurrences are in the lower part 
of the Upper Division of the Series. 
NOTE 19. 
(Page 224, line 14 from top of page.) 
ERRATUM. 
T, 40 should read T. 49. 
NOTE 20. 
(Pages 253-258.) 
THE UNCONFORMABLE CONTACT OF BLACK RIVER, DOUGLAS COUNTY, WISCONSIN. 
The quotations here given from Mr. Sweet’s descriptions of this contact are per- 
haps not extensive enough to bring out all the important facts. As the occurrences on 
Black River and on the other streams of the vicinity have a very considerable impor- 
