STATE GEOLOGIST. 15 



(6) Blue clay with iron pyrites. (Douglas, 1841, 



pp 109.) 

 (a) Light blue limestone. 

 B. Black bituminous limestone. (Douglas, 1841, pp. 



102, 103.) 

 A. Blue limestone. (lb.) 

 XI. Mackinac limestone, (Douglas, 1841, p. 102, 103,) — 



" Manitoulin Portion of Upper Limerock." (Hough- 

 ton, 1840, pp. 19, 21.) 

 X. Polypiferous Portion of Upper Limerock. (Houghton, 



1840, pp. 19, 21. 



IX. Pentamerus Portion of Upper Limerock. (lb.) 



VIII. Lower Limerock and Shales. (Houghton, 1840, p. 16.) 



VII. Sandy Limerock. (Houghton, 1841, p. 20.) 



VI. Upper grey Sandstone. (Houghton, 1841, p. 19.) Not 



conformable with next stratum. 

 V. Lower, or Red Sandstone and Shales. (Houghton, 



1841, p. 119.) 



IV. . Mixed Conglomerate and Sandstone. (Ib.)A 



III. Conglomerate. (lb. 1T.)b 



II. Metamorphic Rocks. (lb. 16.)c 



I. Primary Rocks. (lb. 15 )d 



Little more than a year after the suspension of the survey 

 under Dr. Houghton, Congress passed an act, approved March 

 1st, 1841, embracing provisions for the geological exploration 

 of the Lake Superior Land District, organized by the same act. 

 Under this act, Dr. C. T. Jackson was appointed by the Secretary 

 of the Treasury, to execute the required survey. 



After having spent two seasons in the prosecution of this 

 work, he presented a report of 801 pages,* and resigned his 

 commission. In the meantime, the survey was continued, and 

 subsequently completed by Messrs. Foster and Whitney, United 

 States Geologists. Their Report, of 224 pages, on the " Copper 



a, b, o. d. The Traps intersect this series variously. 



*Ann. Mess, and Doc. 1849-50, Part HI. Also, Senate Doc. 1st Sess. 31st Cong. Vol. 3, 

 1S49-60. 



