MAGNETIC OXIDE OF IRON. 
87 
titles of the worn and rounded fragments cover the shore. It forms a beautiful material for 
garden and door-yard walks, and ship loads of it might be transported to any part of the lake. 
The examination of the beach formed of this material, exhibits a curious example of the 
power of the waves to sort and collect the pebbles ; those, for instance, of a given size, are 
gathered together, separated and placed by themselves. All the large ones occupy places 
distinct from the smaller ; and in using them for walks, we have only to select the size we 
wish for the object in view. 
There are no facts connected with the porphyry of Essex, by which its character as a 
mineral bearing rock is revealed, except, indeed, those of a negative kind : no rock of this 
character is found in connection with mineral veins or beds, in the northern counties. 
In giving the extent of this rock, I have supposed it to have been once a continuous mass, 
and to have extended from Cannon’s Point to Rattlesnake’s den, a distance of about five miles. 
This, however, is a matter of conjecture, and the opinion is founded upon the perfect simi¬ 
larity of the rock at all the intermediate places where it is to be seen. 
I would take this occasion to recommend to students in geology, to visit the shores of Lake 
Champlain. It is a field full of interesting and instructive phenomena ; one in which the 
dynamics of geology may be studied to the best advantage. Moreover, the field is quite 
accessible, and every part may be visited at an expense not disproportionate to the advantages 
which may be obtained. 
3. Magnetic Oxide of Iron. 
Reasons for placing the oxides of iron among the rocks. — State of oxidation accidental. — 
Form in which the two oxides occur among the rocks. — Masses and veins. — Appearance 
of stratification. — Association of garnet with veins of magnetic oxide, etc. 
On account of the great extent of the oxides of iron in the northern counties of New-York, 
I have considered them deserving of a place among the rocks ; and as they resemble, in their 
mode of occurrence, the trap, greenstone and porphyry, I have arranged them all together. 
By this course, I do not mean to maintain that the resemblance is complete ; it is, however, 
sufficiently near to admit of their being placed in juxtaposition. It will be perceived that I 
have kept the two oxides of iron distinct; though in this there appears to be no very good 
reason, for the state of oxidation is to be regarded as an accidental circumstance, rather 
than one which is fixed and necessary. It is true, undoubtedly, that the magnetic oxide is 
formed of definite proportions of its elements originally, but it is liable to change, and pass 
to the state of a peroxide ; to become, in fact, so far as its composition is concerned, the 
specular oxide ; and it will probably appear, on a careful analysis'-of the magnetic ores, as 
they exist in their beds, that some considerable diversity exists as it regards the proportion of 
oxygen in combination with the iron. Besides this, their mode of occurrence geologically is 
not very different. The collective facts derived from both oxides as they exist in the earth, 
when taken together, constitute but one class of phenomena, or bring out and establish but 
