OF THE NORTHWEST. 



61 



previously been done in exploring for metallic veins, the geologist has to draw his 

 conclusions from general principles, from numerous geological observations, and 

 from comparisons with other mineral regions ; also, from precedents established by 

 experience, and recognised by those best versed in the history and statistics of 

 mining. 



It has been shown, in my Eeport of 1839, that the mineral-bearing property of a 

 geological formation depends on its lithological character, on its geological position, 

 and on the disturbing forces which have acted on it from beneath, in lines of dislo- 

 cation, especially when these are accompanied by intrusive rocks. 



The Lower Magnesian Limestone, as it presents itself north of the Wisconsin 

 River, has many characters which indicate a metalliferous rock. It occurs, as we 

 have seen, in thick and solid walls, massive and durable ; it is traversed by rents 

 and fissures of determinate course, of which the walls have but little disposition to 

 crumble and give way ; it is intersected by spars, crystallizations, and vein stones, 

 such as usually accompany metallic ores. Along certain parts of its range, it bears 

 evident marks of considerable local disturbance, the signs of an adjacent axis of 

 dislocation. It has, as already shown, many points of analogy with the Upper 

 Magnesian Limestone of the Mineral Point and Dubuque districts of Wisconsin 

 and Iowa, — a rock which has proved itself to be extraordinarily productive in lead 

 ore,* and has afforded copper ore of excellent quality, which is now smelted, with 



* My estimate of the annual produce in lead from the mines of the Mineral Point and Dubuque 

 districts, for the year 1839 (Senate Doc. 407, 28th Congress, 1st Session, p. 45), was thirty millions of 

 pounds. To the correctness of that estimate, thought by some, at the time, extravagant, subsequent 

 shipments of lead from these mines testify. 



Mr. James Carter, of Galena, has kindly furnished me with a statement of the actual recorded ship- 

 ments from these mines, from February to December, in the years 1841, '42, '43, '44, '45, '46, and '47- 



SHIPMENTS OP LEAD FROM GALENA AND DUBUQUE, AND ALL OTHER POINTS ON THE UPPER MISSISSIPPI, 





FOR 



THE YEARS 1841 



'42, '43 



'44, '45, 



'46, '47, 



'48, '49, 



'50, AND 



'51. 









Pigs Lead. 



Pigs Lead, 



Pigs Lead, 



Pigs Lead, 



Pigs Lead, 



Pigs Lead, 



Pigs Lead. 



Pigs Lead, 



Pigs Lead, 



Pigs Lead, 



Pigs Lead. 



MONTHS. 



1841. 



1842. 



1843. 



1844. 



1845. 



1846. 



1847. 



1S4S. 



1849. 



1850. 



1851. 



January. . . . 

























February, . . . 











5,287 















March, .... 



4.0S0 



80,125 





78.636 



97.746 



28,841 



15,669 



39.170 



38,615 



52.311 



27,379 

 71,056 



April 



91,290 



65,080 



73,449 



82.737 



104,558 



126.073 



82.231 



102.601 



71,234 



81,642 



May, 



91,233 



46,515 



122224 



89.982 



93,623 



142.489 



119,391 



109,235 



84,396 



86.662 



71,903 





57,110 



37.959 



74.475 



80.784 



87,058 



113,209 



185,084 



103.092 



101.090 



88,189 



July, 



58,820 



54,436 



77.333 



66,699 



68,153 



S3.559 



110,3S3 



83,0L1 



77,604 



52755 







37,257 



43,250 



67,233 



55,200 



107,957 



50.257 



61,462 



70,595 



66.345 



37.957 





September, . . . 



16.092 



39,081 



45.400 



54.203 



63,424 



58,827 



67.761 



63.278 



46,798 



55,048 







46,286 



54,941 



67.473 



63,072 



78,887 



71,668 



63.825 



69.16S 



74,207 



59,740 





November, . . . 



50,640 



26,472 



33.734 



53,288 



71,767 



54 291 



65,873 



40.095 



65.174 



55,217 





December, . . . 













1.500 







3.471 







Total 



452,814 



447,859 



561.321 



624,601 



77S.460 



730.714 



771,679 



680,245 



628,934 



509,521 





First arrival of 

























steamboats, . . 



March 22 



March 9 



April 15 



March 5 



Feb. 26 



March 10 



March 29 



March 11 



March 15 



March 9 



March 14 



Last departure of 























steamboats, . . 



Nov. 22 



Nov. 16 



Nov. 26 



Nov. 21 



Nov. 23 



Dec. 2 





Nov. 24 



Dec. 4 



Nov. 28 





As a pig of lead will weigh, on an average, seventy pounds, it appears from the above table that the 

 annual produce has varied, in the last ten years, from nearly thirty-two millions to upwards of fifty- 

 four millions of pounds. 



The decrease in the production of 1848, '49, and '50, is in part attributable to the number of volun- 

 teers in the Mexican war, and in part to emigration to the gold mines of California. 



