122 On the most proper Means of [Aue. 



necessary to prove that all the lava surrounding these lakes is of 

 the same nature, but different from the compact lava of mount 

 Albanus. A few observations which I made seem to show this. 

 The lava of the two lakes is very compact, and usually destitute of 

 those pores which distinguish the lava of mount Albanus, so that 

 it cannot be distinguished from the most compact basalt. The lava 

 of the lake Albanus only contains large leucites ; but that of mount 

 Albanus contains likewise innumerable small ones. The lava at 

 the west gate of Ncmi is destitute of leucites, and contains instead 

 of them small crystals of felspar. But no such crystals can be 

 seen in the lava of mount Albanus. These observations I admit 

 are too few to determine the point. It would be necessary to in- 

 stitute a minute comparison between the lava surrounding the 

 lakes, and that of mount Albanus. 



The stone containing haiiyne is found in the whole peperino, 

 and often in the earthy soil seemingly formed by the destruction of 

 peperino. Thus it is found at ftemi, Gensano, Albano, near 

 Tusculum, and at Rocca di Papa. 



But it is for the most part collected in the great peperino quarries 

 below the town Marino. From this place I obtained the specimens 

 which 1 subjected to examination. 



Haiiyne, dark green mica, augite both crystallized and in 

 grains, a white mineral, and oxide of iron, mixed in various pro- 

 portions, constitute this stone. Sometimes the white mineral is 

 wanting, the proportion of mica is greatly increased, and the 

 haiiyne acquires a green colour. Sometimes mere dots of blue 

 haiiyne are to be observed scattered through the white mineral, 

 and in that case the mica is very scanty. The proportion of augite 

 is usually small, and its particles are often so minute as scarcely 

 to be determined by the naked eye. The oxide of iron is less 

 abundant than the augite. It is often partially converted into red 

 oxide of iron. 



Article VIII. 



Memoir on the most proper Means of accelerating the progress 

 of' Mineralogy. By M. T. C. Braun Ncergaard. Read to 

 the First Class of the French Institute in Nov. 1812. 



The question has been often asked of me, whether, after 

 having seen so many minerals during my travels, and being in 

 possession of a collection as excellent for the choice of the spe- 

 cimens as instructive in consequence of the numberless suites 

 which it contains, I had any intention of ever publishing a 

 System of Mineralogy ? My answer has always been in the 

 negative. It was not dictated by that false modesty, which often 

 injures the progress of science, and which would not have 

 blinded mc so far as to decline a career so flattering to my 



