1850.] DAWSON METAMORPHIC ROCKS OF NOVA SCOTIA. 359 



The walls of the vein are not seen at this place ; but 1 50 paces south 

 of the first trench, a thick dyke of greenish igneous rock, apparently 

 a very fine grained greenstone, appears, with a course of S. 102° W. 

 This dyke is not seen westward of this place, but it can be traced for 

 a considerable distance to the eastw^ard. In the Mill Brook, two 

 miles east of Folly River, it appears in connection with a bed of black 

 slate near the margin of the metamorphic system, and probably a 

 continuation of that seen in a similar position in the Folly and Great 

 Village rivers. At the Mill Brook, the dyke is about 100 feet in 

 thickness. 



In the bed of the Mill Brook, the vein is seen in the form of a net- 

 work of fissures chiefly filled with ankerite ; and in its eastern bank 

 it attains a great thickness. In the bank of another brook still 

 farther to the eastward and in the same line of bearing, it appears to 

 be of large dimensions, and contains abundance of red iron ore and 

 red ankerite. I have not traced it further to the east, but I have no 

 doubt of its continuance to a great distance in that direction. 



I shall now present a few facts and inferences bearing on the 

 manner in which this deposit may have been produced. 



The ferruginous magnesian limestone which I have named ankerite, 

 differs somewhat in composition from the European specimens on 

 which that species was founded. The mean of two analyses which I 

 have made of specimens from the Folly River is, — 



Carbonate of lime 54*6 



Carbonate of iron 23-2 



Carbonate of magnesia 19"5 



Silica 27 



100-0 



Specimens from other parts of the vein, which I have examined qua- 

 litatively, contain the same substances ; the red ankerite having in 

 addition a variable proportion of the peroxide of iron. The specific 

 gravity of a specimen from the Folly River is 2*916, that of a spe- 

 cimen from the Acadia Mine is 2-997. The other external characters 

 of these specimens correspond with those of ankerite. Perfect uni- 

 formity of composition in compounds of this kind from different lo- 

 calities can scarcely be expected, and indeed where the constituents 

 are so nearly isomorphous, species founded on chemical characters 

 must graduate into each other. For this reason, although my speci- 

 mens are destitute of the small percentage of manganese found in 

 European specimens of ankerite, and differ somewhat from these latter 

 in the proportions of their other ingredients, I have thought it advi- 

 sable to refer them to that species. Even if the absence of manga- 

 nese, or any external differences which may be found on a comparison 

 with European specimens, should hereafter be considered sufiicient to 

 establish a specific distinction, my application of the name ankerite 

 can, with the above explanation, lead to no misconception. 



The absence of cavities and ^ combs ' in the ankerite, its pretty 

 uniform coarse granular structure, its perfect penetration of all the 



