44 THE CANADIAN NATURALIST. [Vol. ix. 



is of sufficient importance to be used as a distinction among 

 kinds of rocks. In the first place, it is trivial as a crystallo- 

 graphic distinction. Secondly, although mineralogy once made 

 much of the distinction, it now makes little of it. Thirdly^ 

 it is not sustained by the analyses of the varieties of foliated 

 pyroxene — diallage and the wrongly called hypersthene being 

 essentially identical in composition with common augite of erup- 

 tive rocks, and the smaragdite, with other crystallized horn- 

 blende. This is shown in any work giving full lists of analyses 

 of minerals, and is well understood ; yet the introduction here of 

 a few of the analyses may not be superfluous. Nos. 1 to 5 are 

 of diallage and pseudo-hypersthene, and 6 to 8 of augite crystals 

 from Etna and Vesuvius. 



Si02 AI2O3 FeO MnO MgO CaO H2O 



1. Florence, X>ta« 53-20 2-47 8-67 0-38 14-91 19-09 1-77=100-49 



Kohler. 



2. Piedmont, i)io/^ 50 05 2-58 11*98 17-24 15-63 2-13 = 99-61 



Regnault 



3. Graubiindten, Dio/^ . 49-12 3 04 11-45 1533 18-54 1-46 = 98.94 



V. Rath. 



4. Harzburg, ifi/i) 52-34 3-05 8-84 15-58 19-18 0-66 = 99-65 



8treng. 



5. Neurode, ^i/j) 5.3-60 1-99 8-95 0-28 13-08 21-06 0-86 = 99-82 



V. Rath. 



6. Etna, Augite Cryst. . . . 50-5-5 4-85 7-06 13-01 22-29 = 98-66 



Kudernatsch. 



7. Vesuvius " .... 50-90 5-37 6-25 14-43 22*96 = 99-91 



Kudernatsch. 



8. Vesuvius " .... 49-61 4-42 9-08 14-22 22-83 =100-16 



Rammelsberg. 



The mineralogical and chemical differences are thus too slight 

 to make the distinction of any lithological importance, and this 

 importance can be sustained, if at all, only on geological con- 

 siderations. 



The particular rock, in the description of which the character 

 stands prominent, is that called Gahhro in Germany. It is well 

 known that this Italian word was the provincial name originally 

 of common serpentine. Ferber, in his "Briefe ausdem Walsch- 

 land " (Letters from Italy), written in the years 1771, 1772, 

 and published in 1773, describes so well the rock near Florence, 

 that we cite briefly from him. He first says, in a letter from 

 Florence, of Dec. 11, 1771 (in which he gives scientific notes on the 

 minerals and rocks of the regions), that the Gabbro of the Italians, 

 occurring in Italy, Tuscany and Genoa, is identical with the 

 serpentine of Saxony. Then, in another of May 23, 1772, he 

 repeats the statement and describes particularly, and with scien- 

 tific precision, the gabbro of Mt. Impruneta, near Florence, and 

 mentions the occurrence in it of a talky, micaceous mineral, 



