AND THE INTENSITY OF MAGNETIC FORCE. 291 
6. Wapsipinnicon River, (lowa,) Latitude 41° 44’, N.; Longitude, 90° 39’, W.; September 25, 1839. 
{09 Duration Calculated ‘Total intensity, 
Dip. | No. of | Epoch of commencing] of 500 |'Tempe-) duration Square ofthe | Horizontal |'Total intensity,|that at Cincin- 
pisedin Vibrations. Vibrations.| rature. | at 60°, preceding. intensity.| Hor. being 1000.|nati being 1000. 
72° 15° | 1 | 9h.04m.59s.6 | 1596, |56° |1596.77|2549674.4329| 928.54 
2 19 59 00 4 | 1574.4/56 5 |1575.02|2481255.0400| 930.89 
3 ILE 12 03 2 | 1280,4/61 7 /1280,27|1639091.2729) 931.04 
Mean,| 930.16| 3051.06 | 1020.61 
Declination, 8° 25’, east. Observed by myself. 
Locality: on the rocky table or upper bank of the river, which was in a channel mode- 
rately deep. Geology: cliff limestone cropping out at bluff banks, but covered generally 
with good soil, prairie and scattered timber. Wind from north-west, blowing by gusts, a 
moderate gale; clouds ragged cumulo-stratus, covering half of the sky, each occupying 
10 to 80 degrees. Sky beautifully blue and clear between. 
7. Iron ore bed, (lowa,) Latitude 41° 55’, N.; Longitude 90° 56’, W.; September 27, 1839. 
72°60'30"| 8 | 8h.51.033.2 A] 1295.2] 49° [2060.4 |1679719.6816] 908.52| 3079.59 | 1030.16 
Declination, 7° 05’, east, (Locke. ) 
Locality, about three quarters of a mile from the Wapsipinnicon river. Surface rather 
uneven. ‘The iron ore in place appeared to be the hydrated peroxide, often hematitic, 
not at all magnetic, but some loose pieces, probably transported, were not only magnetic, 
but actually possessed polarity. 'The magnetism of this place, it appears, is peculiar, the 
dip and intensity being both greater than the latitude elsewhere exhibits. 
8. Milk at Brown’s Settlement, Latitude 42° 02’, N.; Longitude 91° 18’, W.; September 30, 1839. 
72°21’ | 4 |11A.10m.04s.0 A] 1603.6)53° [1605,. (2576025. 919.05) 
2 |11 54 00 4A} 1586.0/55 5 |1587.03/2518664.2209] 917.07 
3 112 40 02 OP| 1289.0157 6 |1289.18)1661985.0724| 918.22 
Mean,| 918.11; 3028.05 1012.92 
Declination, 9° 10’, east, (surveyors;) 9° 04’, by my own observation. Locality, in a 
valley. 
9. Branch of the Makoqueta River, Latitude 42° 14’, N.; Longitude 91° 09’, W.; October 2, 1839. 
72°43'37"| 38 | 9h.40m.02s.0 A] 1300. | 64° [1299.7 | 1689220.09 | 903.41} 3042.57 | 1017.77 
Declination, 8° 45’, east, (by surveyors.) 
Locality, near a bluff or cliff limestone thirty feet high. Weather clear and fine; a 
few cirrus clouds. 
10. Farmers’ Creek, (lowa,) Latitude 42° 13’, N.; Longitude 90° 39’, W.; October 5, 1839. 
913.24 | | 
72° 86’ 1 [12h.438m.018.2 P| 1613.2/76° 1610.1 |2592422.01 
2 1 21 O11 6 P| 1594. |83 28)1588.7 |2522867.69 | 915.54 
3 3 52 00 8 P| 1292.4)66 1291.95)16691384.8025) 914.29 
Mean,| 914.36 
8057.64 1022.82 
Declination, 9° 11’, east, by my own observation, and 9° 4’, by United States survey- 
ors. High tables of cliff limestone cut deeply, and abruptly, by the streams, characterize 
VOL. IX.—77 
