92 Deposits op phosphate of lime. tftuttuft 
Ft. In. 
f 4. Blue, yellow, and coarsely mottled plastic clay, with scattered coarse 
quartz aud other sand grains and numerous sandy concretions 2 
5. The "silt bed," a chocolate-brown and yellowish sand, passing into a 
sandy clay, which is rather coarse, loose, and like an ordinary shore 
sand. It consists principally of quartz and iron grains. This bed 
passes gradually into bed 4 * * 2 
6. The "upper coprolite seam," a pebble bed of phosphatic nodules, Lyd- 
B<( ian stone, chert, quartz, aud other pebbles as big as beans packed in 
loose, iron-colored sand. Some irony concretions occur in its upper 
part, where it passes into bed 3 2 
The "lower coprolite seam," a thin band where the coprolites are 
darker and better than in the upper seam. The sandy matrix is 
hardened almost to a rock by carbonate of lime, which was probably 
derived from the underlying bed (a) 3 
f A calcareous grit of coralline age. It is a hard, gritty, bedded lime- 
C^ stone, gray colored, with scattered large oolitic grains; no fossils 
I seen . 
Iii the last section the nodules are darkest near the base. The phos- 
phatic and siliceous pebbles are in about equal quantities. Silicified 
wood, ferruginous concretions, and hard lumps of clay are numerous. 
The nodules contain more alumina than those of the Upper Greensand 
(Walker). 
The nodules proper of the phosphate beds are of a very variable 
character, in which respect they resemble the nodules of North and 
South Carolina. They vary in size from pieces no larger than a grain 
of sand to masses weighing 3 or 4 pounds. They give off an organic 
smell when rubbed, have a cubic fracture, and vary from yellow to 
chocolate brown in color. Their hardness is 3 to 4. The darker nodules 
are near the bottom of the bed; though, in most cases, the color depends 
on the substance originally phosphatized (Keeping). The nodules some- 
times are of a perfectly homogeneous and opal-like nature. From this 
they go through all stages of sandiness, till they are simply nodules of 
phosphatic sandstone. Keeping, in describing them, says: 
There are certain curious branching, interlacing, undulating, or simply straigbt- 
crossing structures forming little gutters over the surface of the nodule, aud canals 
penetrating into its substance. * * * Some of these are mere shrinkage cracks 
and others are the marks of where " episites, " such as Serpulce and Polyzoa, have been 
attached to the inner surface of the original shell ; others again are probably the 
work of boring creatures, especially sponges, but the great variety and many pecul- 
iarities of type that occur and their constant association with phosphatic nodules 
are facts not sufficiently explained by the accumulated work of all the above-men- 
tioned agents. 1 
These nodules are not so rich in phosphate of lime as those of the 
Upper Greensand; they average 40 to 50 per cent. (Volcker), while 
those above the Gault average 50 to 60 per cent., phosphate of lime 
(Way). (See analyses.) 
1 This exactly describes the surface of many of the phosphatic nodules of the Ala- 
bama Cretaceous formation. 
(56G) 
