296 Scientific Geology, 



to suppose it older than the encrinal or transition limestone ; and that 

 it formed a bed in the argillaceous slate of Bernardston, which ap- 

 pears to be one of the oldest varieties of that rock. But its organic 

 remains settle the question of its position ; and differing in dip and 

 direction from the slate, I have been led to doubt whether it really 

 forms a bed in that rock. The slate in the vicinity runs nearly north 

 and south, and the dip is nearly 90 ; but the limestone runs N. E. and 

 S. W., and dips S. E. not more than 20. Besides, the rock that is 

 found above the bed of limestone, (No. 601,) appears to be mostly 

 composed of quartz, and probably ought to be called quartz rock. 

 It does not lie in immediate contact with the limestone, nor is the 

 slate visible immediately beneath the limestone. Upon the whole, I 

 am of opinion that this limestone lies beneath the oldest variety of 

 the new red sandstone series, which has been described, and upon the 

 argillaceous slate, in an unconformable position. Probably further 

 research might settle this point satisfactorily. 



Two species of iron ore occur in this limestone ; the magnetic ox- 

 ide, (Aimant, Beudant,) and the bog ore, or hydrate of iron, (Limo- 

 nite ocreuse, Beudant.) The latter is disseminated through a large 

 proportion of the upper layers of the limestone, and also forms masses, 

 several inches thick, between these layers. It exactly resembles the 

 common bog ore, so abundant in our alluvial formations. (No. 504.) 

 This is not the only instance in which I have found this ore between the 

 strata of other rocks, as I shall have occasion to show hereafter j and 

 Beudant mentions several localities in Europe, where the limonite is 

 found "between the beds of divers rocks." 



The magnetic oxide occurs as a bed in the limestone, lower down 

 than the bog ore. The bed follows the dip of the limestone, and that 

 rock is much impregnated with the ore in the vicinity ; so as some- 

 times to produce a sort of brecciated marble. (No. 472.) 



It is very obvious that both these species of iron ore must have been 

 of contemporaneous production with the limestone, since it is impos- 

 sible to conceive how parallel interstices could have existed between 

 strata so little inclined, long enough to be filled by watery infiltration, 

 or igneous sublimation, or galvanic agency, the only modes by 

 which metallic repositories have been supposed to be filled. That the 

 bog ore was deposited, as we find the same ore now forming, seems 

 highly probable. But I am not aware of any theory which will sat- 

 isfactorily explain how the magnetic oxide, which consists of 69 parts 



