Geological Survey of the Great Canal. 373 



gard every new step of this kind, as an addition to our na- 

 tional resources. 



Excepting the natural alum of the caverns in Tennessee 

 and of some other regions of the West and South, and that, 

 occasionally found, in our schistose rocks, and used in these 

 cases, more or less, for domestic dyeing, and other purposes, 

 we were not aware that the United States possessed any re- 

 source for this article independent of the foreign markets. 



Some time since, we were informed that a manufactory 

 was established at Salem in Massachusetts, and the proprie- 

 tors have recently put us in possession of a set of specimens, 

 which prove that the effort has been completely successful. 



Among the crystals of alum, are some of great size, and ex- 

 quisite beauty and transparency, exhibiting to the naked eye, 

 in a very striking manner, the successive layers of super-posi- 

 tion and the progressive increments and decrements. A part 

 of an octaedron lies before us, complete, except on the side 

 where it adhered to the mass. It measures nearly five inches 

 by four, and has the most perfect finish on its faces, and solid 

 edges and angles, which are in every part, replaced by trun- 

 cations. Some crystals of rather smaller size are quite or 

 nearly perfect. We are aware that fine crystals of alum are 

 not rare in manufactories, but we have not seen these equal- 

 led even by the similar productions of the celebrated establish- 

 ment near Glasgow. There can be no question from the 

 appearance of these crystals, as well as from that of the 

 amorphous masses, of the extreme purity of these materials. 

 Perhaps they are even purer for this reason, that the alum is 

 not manufactured (as we understand,) from the usual source, 

 namely, the decomposed alum slates, but from the direct syn- 

 thetical union of sulphuric acid with the argillaceous earth. 



The sulphate of copper, (blue vitriol,) made at this estab- 

 lishment, is equally perfect in its kind, presenting crystals of 

 extreme finish and beauty. 



The skill manifested in the manufacture of these articles, 

 clearly evinces, that the persons conducting this establish- 

 ment, are quite equal to the task which they have underta- 

 ken, and are fairly entitled to the public confidence. — Ed. 



10. Geological Survey on the Great Canal. 



The patroon of Albany, the Hon. Stephen Van Rensse- 

 laer, with his usual liberality, has undertaken the expense of 



