158 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [ Dec. 22, 
hard chalk of 125-5 feet, the remaining 78 feet of basalt being hard, 
compact, and columnar. No iron-ore is exhibited in this series. 
4, Metamorphism of Bole, and origin of the Pisolitic ore.—The 
spheroids of iron-ore are powerfully attracted by the magnet; and 
the following analysis by Dr. Apjohn proves that the iron is in 
the states of per- and protoxides. The source of the iron is to be 
sought for in the hydrous peroxide of the bole, originally in com- 
bination with the silicated minerals of the basalt, and probably also 
in the hydrous oxide resulting from the decomposition of included 
magnetite and iron pyrites. 
Analysis of Spheroids from Pisolitic ore, Red Bay. 
Magnetic oxide of iron —.......08..-..4--- 11°74 
TEE RORACLS) OE KOM soso coonsacadosoncHeqgoNsNNoDS 51:37 
Silica, alumina, &e. (by diff.) ............ 36°89 
100-00 
Percentage of metallic iron ............... 44:45 
If we compare the analyses of basalt and ochre (given on p. 156), 
with those of the iron-ores (p. 159), we shall not fail to notice 
the general similarity between them ; the chief differences observ- 
able are the proportions of the several constituents, and, in the 
case of the pisolitic iron-ore, the different degrees of oxidization of 
the iron. But these differences do not militate against the pre- 
sumed origin of the bole and iron-ore—that they are several stages 
in the metamorphism of one original mass: the addition of water to 
the basalt, and loss of lime, other alkaline earths, and alkalies, pro- 
duced bole; the loss of water and oxygen from the ferruginous 
materials of the bole resulted in an increased percentage of iron in 
the pisolitic ore. Though aqueous agency may have effected the 
first change, it could not have produced the second; and heat is the 
force we must call to our aid in the alteration and concentration of 
the oxides of iron; and by it the phenomena exhibited by the iron- 
band are then easy of explanation. We assume that the under- 
lying bole or ochre was a wet or sodden terrestrial surface ; in fact 
many circumstances necessitate such a condition ; and the subsequent 
overflow of basalt effected, by its heat, pressure, and possibly evolved 
gases, a reduction of the contained oxides of iron into the more 
concentrated form in which they occur in the iron-band, the aggre- 
gation of the ferruginous particles being a result of the same ac- 
tion *. This metamorphism is analogous to the development of new 
minerals by the intrusion of igneous masses among schistose and 
stratified rocks. It will be observed that the accumulation of the 
oxides of iron to certain centres diminishes as we recede from the 
exciting cause. 
* Since the reading of this paper before the Society, we have examined a 
large number of the spheroids from the pisolitic bed, but once only found dia- 
toms of the Coscinodiscus type, and not of the genera which form the bog-ore: 
they might have got there accidentally. 
