ON THE UPPER MISSISSIPPI. 501 
Upper Mississippi, as every layer, from near the base of the coarse Lingula grit and 
Obolus grit, up to the base of the Lower Magnesian Limestone, admits of being traced 
out as follows: 
1. Coarse Lingula and Obolus grit, especially fossiliferous, towards the top, . 104 
2. Green sand and soft green sandstone, with Trilobites, é : : 6 
3. Soft thin-bedded, green, micaceous sandstone, : : ; 3 14 
4. Brown sliniaaemniies rook; is< x . ‘ 4 
5. Thin layers of green sandstone, ‘ideas with ‘green ah ‘ . 36 
6. Micaceous sandstone with Trilobites. D. Miniscaensis, . : ‘ 2 
7. Alternations of green and ferruginous sandstone, . : : saplectae 
8. Micaceous sandstone, with D. Miniscaensis, : : : : 2 
9. Loose green sand and soft green sandstone, : é , 15 
10. Green and red sandstone, charged with silicate of iron,  . ; ¢ 5 
11. Six inches of bluish-green earth. 
12. Thin-bedded green and yellow sandstone, 30 
13. Band of coneretionary red and yellow sandstone, wid Me off iron aie 
seminated 3 
14. Green, red, and yellow, bimini sngheneide, with thin delosiitis tayens pass- 
ing downwards into siliceo-caleareous rock, d 40 
15. Yellow and ash-coloured argillo-calcareous layers, with D. Diceonteloiiate , 9 
16. Alternations of thin-bedded, light brown, and ash-coloured sandstone, . 6 
17. Thick beds of soft peligwiak sandstone, Xc., as at the Great Slide, ; 50 
18. Mammillary and botryoidal layers, ; ; 2 
19. Quartzose sandstone, with intercalations of biigsiectats bhnelstine; ; ‘ 80 
433 
The top of bed No. 1 is almost made up of Lingulas and Obolus, and five feet 
above the fossiliferous layers, the gritstone contains the same species of Trilobite 
that occurs in the third Trilobite bed, but the rock was so friable that it was almost 
impossible to preserve specimens. The upper and lower divisions of the third Trilo- 
bite bed are here separated by twenty feet of green sandstone, alternating with 
green earth ; the species in both members are, however, the same, and there appear 
to be at lous three different species. Associated with them is a nearly circular 
species of Orthis, and a small Lingula. The Trilobite beds are mostly easily 
cleavable gritstones, of a grayish-green colour, until exposed to the weather, when 
they assume a pale buff hue, and become harder. 
Five miles below Mountain Island, a fine-grained, yellow sandstone, charged with 
Obolus Appolinus, contains also a minute species of Trilobite; the head has a thick- 
ness of about four feet, and underlies the coarse Lingula grit, numbered 1 in the 
last section. These strata have a slight dip here to the northwest, and can be 
traced for a mile down stream ; and near the termination of the exposure the forked- 
tailed Trilobite was observed associated with the above-mentioned fossils, but it is 
difficult to procure good specimens here, owing to the soft nature of the rock. This 
latter Trilobite has not been observed in any of the higher Trilobite beds. The 
Obolus Appolinus, which occurs here in great profusion, associated with these Trilo- 
bites, has even the nacre preserved with much of its original lustre and colour. 
These layers also furnished two species of Lingulas, one of which, a large oval 
