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 Report 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 
* 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 OF LEAD FROM GALENA AND DUBUQUE, AND ALL OTHER POINTS ON THE UPPER MISSISSIPPI, 
FOR THE YEARS 1841, ’42, ’43, 44, ’45, 746, °47, ’48, 749, °50, anv ’51. 
Pigs Lead,|Pigs Lead, Pigs adn Lead,|Pigs Lead,|/Pigs Lead, Pigs Lead,|Pigs Lead, Lead,|Pigs Lead, Pigs Lead, 
bares 1841. 1842. 1843." | 1844, 1845, 1846, 1847. 1848. was 1850. “1851. 
February — 5,287 — — Hee ete 
M 4,080 80,1 97,746 5,669 39,170 38,615 52,31 27,379 
oS ae 91,296 080 | 73,449 | 82737 | 104,558 | 126,073 1 | 102.601 | 71,234 | 81,642 | 71,056 
ae Sg ee 3233 122.224 89. 93,623 9 119,391 109,235 84, 86, 
PONG a=) wise & 67,110 37,959 74,475 80.784 87,058 113,209 185,084 103.092 101.090 88,189 
Ju 58,820 54,431 77,333 9 153 5: 83,011 77, 52.755 
A 37,257 250 67,233 55,200 107,957 50,257 61,462 70,595 66,345 37,957 
September, 16.092 89,081 5) 5 424 58,827 67,761 278 46,798 55,048 
October,. . . .| 46,286 54,941 67,473 63,072 78,887 71,668 63.825 69,168 7 59,740 
vember,., . . 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 a 
eed 3 | 452,814 | 447,859 | 561,321 | 624,601 | 778,460 | 730,714 | 771,679 | 680,245 | 628,934 | 569,521 | 
First arrival of | | 
steamboats,. .| March 22|March9 | April15 March 5 | Feb. 26 March 10 March 29 | March 11 | March 15 | March 9 | March ce 
Last Sezentoes of in | | 
steam boats, Nov. 22 |Nov.16 (Nov. 26° Nov. 21 | Nov. 23 | Dec. 2 on 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 poun nds. 
The decrease in the production of 1848, ’49, and ’50, is in part eo pearl to dow number of volun- 
teers in the Mexican war, and in part to emigration to the gold mines of Califo 
