No. 8.] VENNOR GALENA IN LAURENTIAN ROCKS. 457 



sures, or great cracks, which probably extend downwards to great 

 depths. The course of these fissures is marked by the occur- 

 rence of doleritic and feldspathic dykes, mineral-bearing veins, 

 or where these do not occur, by the abrupt faulting of the strata 

 at numerous points along a number of straight and parallel lines. 

 With these are connected all of the galena veins of Rossie, 

 Lansdowne, Storrington, Loughboro" and Bedford, as well as 

 those in Madoc. Marmora, .Tudor and Lake in Hastings County, 

 and Belmont, Methuen, and very probably also Galway in Peter- 

 boro' County. Thus the westward extent of this great belt of 

 fissures from Bedford cannot be less than 100 miles, and from 

 Rossie 150 miles. In this distance they traverse a succession of 

 strata of very varied characters, cutting alike the gneisses, schists, 

 diorites and crystalline limestones, and at Ringwood, N. Y., 

 the Potsdam sandstones. Of these rocks, the crystalline lime- 

 stones appear to exert the most favorable influence on the lodes, 

 as it is in these they attain their greatest proportions and yield 

 the most ore; while in the alternating gneisses and diorites, par- 

 ticularly where these are of a firm texture, they not only narrow, 

 but in many instances are filled with difierent minerals, such as 

 blende, copper pyrites, mispickel, and more rarely gold, silver, 

 and bismuth. It is this enlargement and improvement of the 

 lodes in the limestones that has given rise to the idea already 

 referred to, namely, that the galena characterizes certain of 

 these bands. The change of mineral contents in lodes of the 

 same age is an interesting and important feature in this con- 

 nection, but it is one that requires much further investigation. 



The direction of most of the galena veins in Lansdowne, 

 Loughboro' and Bedford, is a little north of west and south of 

 east, but varies from N. 85'-' W. to N. 15^ W. In this same 

 direction run all the lines of faulting and most of the intrusive 

 dykes; but these last run rather by short zig-zags than in direct 

 lines. It is an extremely difficult matter to follow out and map 

 any one of these lines continuously through the contorted Lau- 

 rentian country, but such an attempt was made, and in two 

 special instances succeeded beyond my expectations. 



While tracing a number of the faults in Loughboro' and 

 Bedford, one was met with towards the centre of the latter 

 township, which, from its being farther removed from^the 

 overlying mass of the Silurian, furnished more marked features 

 by which it could be followed. This was traced by abrupt dis- 



