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The Daguerreotype and its Applications. 137 
silicious as to render it unfit for burning, and again ‘ containing 
large quantities of imbedded chert,” and it constitutes the island of 
Mackinac, and several others in the vicinity, and rises from one 
hundred and fifty to two hundred and nineteen feet above the lake. 
It “consists: of an irregular assemblage of angular fragments, 
united by a tufaceous cement,” and is not, as has been supposed 
by some, a “conglomerate,”—but “ the rock occupies, no doubt, 
very nearly its original relative position, and its present condition 
may be ascribed to an uplift of the strata, subsequent to its com- 
plete induration, and the fragments have been imperfectly cement- 
ed together.” This rock is regarded by Prof. Shepard, (Am. Jour. 
Vol. xxiv, p. 144,) as the magnesian limestone of Ilinoisand Wis- 
consin, which near Rockwell, (p. 154,) “ almost exactly resembles 
the metalliferous limestone of Missouri, having its peculiar buff 
color, and like it embracing silicious seams and nodules.” 
Its inclination is northwest. In following the eastern shore of 
Lake Michigan, the limestone continues the foundation rock. In 
a future notice we hope to be able to give a more exact account 
of the geology of the state. 
_——— 
Arr. XV.— The Daguerreotype and its Applications ; by W. H. 
Goong, late Chem. Assist. in the Univ. of New York. 
Soon after the introduction of the D g type into this 
country, a number of persons occupied themselves with this 
method of obtaining photogenic pictures. As, however, all the 
Manipulations were to be learned from the printed account of the 
Process, a variety of experiments were performed with a view to 
its abridgment ; some of which led to important results. ‘The 
apparatus has been improved ; the process itself, changed in one 
essential particular ; and important applications have been made 
of this beautiful art. A sketch of these improvements and appli- 
cations may not be uninteresting. 
Pictures of the largest size—eight inches by six—are taken 
with the French achromatic lenses, perfect throughout ; the parts 
Within the shade are brought into view, distant objects are per- 
fectly delineated. A common spectacle lens, an inch in diameter, 
‘of fourteen inches focal length, adjusted by means of a sliding 
tube, into one end of a cigar box, answers very well to take 
Vol. x1, No. 1.—Oct.-Dee. 1840, 18 
