The Daguerreotype and its Applications. 137 



silicions 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. xxxiv, p. 144,) as the magnesian limestone of Illinois and 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. 



Art. XV. — The Daguerreotype and its Applications ; by W. H. 

 GooDE, late Chem. Assist, in the Univ. of New York. 



Soon after the introduction of the Daguerreotype 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 

 ttibe, into one end of a cigar box, answers very well to take 



Vol. XL, No. 1.— Oct.-Dec. 1840. 18 



