ADIRONDACK MAGNETIC IRON ORES 47 



blende, biotite, apatite and magnetite. It has a more or less 

 gneissoid appearance, and the feldspar which originally existed 

 in porphyritic crystals has been considerably crushed, but the 

 textural relations are those of a plutonic igneous rock. It is regu- 

 larly jointed and weathers out into massive blocks. In the Knob 

 mountain area there are included fragments of the sedimentary 

 hornblende gneiss which it has invaded. The Hammondville 

 gneiss to the west is penetrated by dikes and irregular masses of 

 granitic material which are probably offshoots from the larger 

 intrusions. 



Pegmatite may be mentioned as of frequent occurrence in the 

 ore-bearing gneiss. In almost all of the pits this rock seems to 

 have been encountered during the mining operations. It forms 

 masses of varying size and shape that blend with the country 

 rock, and is quite often associated with the ore. 



Distribution and stratigraphy of formations. The Hammond- 

 ville gneiss occupies a compact area about 2 J miles long from 

 northeast, near Dudley pond and its outlet, to southwest where 

 it extends to within a short distance of Burnt Mill brook. Its 

 width is about i| miles. On the north it is cut off by the intrusion 

 of anorthosite and gabbro that stretches over many square miles 

 in an unbroken mass. On the other sides it is in contact with the 

 sedimentary series which occupies the valleys of Paradox creek 

 on the west, Burnt Mill brook on the south and most of the broad 

 ridge between Knob mountain and Penfield pond in a connected 

 belt. The Skiff mountain gneiss which is of the same type lies 

 across the valley of Burnt Mill brook and is thus completely sepa- 

 rated from the Hammondville area. The contact between the 

 sedimentary and ore-bearing gneisses on the north side of Skiff 

 mountain appears to be well up on the slopes. 



The main granite area in the district is found on the ridge east 

 of Hammondville. It takes in the rounded prominences known 

 as Knob and Little Knob mountains, forming an irregular mass 

 or boss intruded in the sedimentary series. Whether it is in con- 

 tact with the Hammondville gneiss to the west could not be defi- 

 nitely determined, but from field observations a belt of sedimentary 

 gneisses would appear to intervene for most if not the entire dis- 

 tance on that side. Both Knob and Little Knob present almost 

 vertical cliffs as seen from the west, suggesting a north-south 

 fault scarp, a feature that was noted by Professor Kemp. There 

 is no direct proof of the existence of faulting at this point, though 

 in a rock cut of the abandoned mine railroad 2 miles north of 



