io6 
examined the specimens themselves, but has made analyses of 
the principal varieties which occur in each class of material. 
The materials of the Ohio pipes and other objects are almost 
exclusively of four kinds ; or rather they may be classed under 
four distinct heads, although two or more varieties of some of 
the materials occur. The materials are sculptured native sub- 
stances, and have not been moulded or fashioned by pressure, 
nor hardened by subsequent baking. I will first name the four 
sorts, and then proceed to describe their individual physical 
and chemical characters : — 
^. A hard and silicious clay slate, approaching more or less 
closely in different specimens the whetslate of Cotta.* 
38. An argillaceous ironstone,! usually variolitic. 
C. A pearly-brown ferruginous chlorite. % 
Ji. Calcareous marls of variable composition, and marly lime- 
stones. § 
Whetslate. 
I have particularly examined a fragment of a " gorget" made 
of this stone (S and D 494). It has the hardness 6*5 on the 
mineralogical scale. Its density is 2*76. On analysis it gave in 
100 parts : — 
Silica (with some alkali) . . 61*35 
Ferrous oxide (protoxide of iron) 14-28 
Alumina ..... 19*33 
Magnesia '33 
Lime ...... 1*34 
Combined water . . . 3*37 
lOO'OO 
This material is a more or less highly silicious variety of clay 
slate, almost perfectly compact, and often very distinctly strati- 
fied with dark bands, in which most of the iron of the rock 
seems collected. It breaks with an irregular conchoidal frac- 
ture, almost without a trace of the peculiar cleavage known as 
* Cotta, * Rocks Classified' (Eng. ed., 1866), p. 265. 
t Dana, ' Mineralogy ' (1868), p. 141. 
X Ibid., p. 495. 
§ Cotta, l.c.^ pp. 272 — 279. 
