ADIRONDACK MAGNETIC IRON ORES 49 



and shearing movements have occurred. The Knob mountain 

 granite, the syenite and the gabbro are frequently gneissoid, it is 

 true, but they preserve recognizable textural characters that leave 

 no doubt as to their relationships. It seems likely, therefore, that 

 the gneiss has suffered greater vicissitudes from compression and 

 other dynamic influences than the igneous rocks due to an earlier 

 period of formation. No apophyses or masses of the gneiss 

 approaching dike form have been found in the adjacent sediment- 

 ary series and contact effects are wanting. On the other hand the 

 gneiss is involved with the hornblende gneiss in a way that is 

 difficult to explain on the theory that the former has been intruded 

 into the latter. Alternating bands of the two rocks occur along 

 the borders of the areas. This feature is particularly well devel- 

 oped south of Hammondville in Burnt Mill valley, where the bands 

 of hornblende gneiss may be observed more frequently as the con- 

 tact is approached. The regularity in width of the bands, their 

 perfect conformity to the strike and their persistency suggest 

 interbedding rather than inclusions caught up by an invading 

 igneous magma. If the view that the gneiss is not an intrusive be 

 accepted, then the rock probably belongs in the sedimentary 

 series. The alternative that it may represent a part of the basal 

 complex on which the latter have been laid down has little claim 

 to attention since on this theory the same difficulties would arise 

 in explaining the contact relations with the sediments that are 

 met by the intrusive theory. The existence of a fundamental 

 system of rocks underlying the limestones anyway has not been 

 established beyond peradventure in the Adirondack region. 



The structural relations of the gneiss are very obscure. Satis- 

 factory readings of dips and strikes are not obtainable over much 

 of the area, owing to absence of those minerals which produce 

 foliation. That the rock has been subjected to intense plication 

 is evidenced by the included pegmatite bands, which are folded 

 and twisted in the most intricate manner, as well as by the struct- 

 ure of the ore bodies hereafter described. The observations of 

 dips and strikes where made point to a concordant arrangement of 

 the ore-bearing gneiss and the sedimentary rocks. The latter as a 

 rule show strikes that follow more or less closely the outline of the 

 area, suggesting that they wrap around and overlie the gneiss, 

 though their inclination seems to be quite irregular. The attitude 

 of the whole series may be the result of a compressed anticlinal 

 fold. 



If originally a sediment the ore-bearing gneiss has probably been 



