APPENDIX TO CHAPTER V. 109 



APPENDIX TO THE TACONIC SYSTEM. 



The origin of the brown licnmlitic iron has been a subject of considerable inquiry ; but 

 very little light has been obtained upon the subject, until recently. Formerly my own 

 opinion in regard to its origin, was, that it originated in a limestone shale, which was 

 charged partly with oxide and partly with a decomposing sulphuret of iron. Such a mix- 

 ture exists throughout the entire range of the formation, and is usually a bed subordinate 

 to the Stockbridge limestone ; besides, the hematite occurs in beds connected with alluvial 

 or diluvial formations, which appear to have been derived from decomposing or disinte- 

 grating masses situated at some distance. I am inclined to maintain the opinion still, that 

 such may have been the origin of many of the beds situated upon the ranges of this sys- 

 tem. During an examination, however, of some of these beds near North-Adams in 

 Berkshire county (Massachusetts) , I foimd tliat the ore might be traced to veins which 

 penetrated into the solid quartz rock or brown sandstone of the Taconic system. This vein 

 is interesting, in consequence of being connected with a peculiar brecciated mass, which 

 consists of sharp angular fragments of quartz cemented by the hematite. The fragments 

 are often enveloped in a layer of hematite of a fibrous structure, or, in other words, in a 

 fine variety of limonite. This investing coat is sometimes half an inch thick, and it 

 frequently cements masses of fragments of great size and weight. The opinion which has 

 usually prevailed in regard to this breccia, is that the rock was broken thus by some cause 

 unknown, and the fragments subsequently cemented together by infiltration of the oxide 

 of iron. This mode of formation is not very objectionable, inasmuch as we frequently see 

 operations of a similar kind now in progress. But we may very profitably inquire whether 

 it is applicable to all cases ; and whether, if we even admit it as true in part, we may not, 

 under certain circumstances, adopt a different view of its origin? The first inquiry is, how 

 came the quartz in this form, broken and even apparently comminuted, and the fragments 

 as sharp and splintery as though they were just broken with a hammer? Pursuing our in- 

 quiries, may we not ask ourselves whether there is any connection between the force which 

 broke the quartz as described, and tliat which effected the cementation subsequently ? As 

 to the Adams vein, in connection with the brecciated mass, the enquiry, taken in connec- 

 tion with the origin of veins, seemed very natural. Thus, adopting the view that veins 

 are rents filled with molten or ignited matter, it appears highly probable that the oxide 

 of iron or hematite might have been forced up from below ; and, when it reached the 

 surface, it may have flowed into the natural joints of the quartz rock, and have farther 

 broken the bed by the sudden application of heat, and hence consolidated the fragments 

 as we now find them. All the known facts which are at all concerned in the incpiiry, go 

 to show the probability of this view of the suliject. Thus, heat applied suddenly to this 

 vitreous quartz would have the effect we have supposed, namely, to fracture it : the filling 



