48 NEW YORK STATE MUSEUM 



Knob mountain a brecciated zone occurs bearing nearly in line 

 with the cliffs. 



The syenite is exposed in force northeast of Hammondville in 

 the vicinity of Overshot and Round ponds. It has the anorthosite 

 on the west, the line of contact following just west of the road 

 toward Dudley pond. A tongue of syenite extends southward 

 from this area into the sedimentary gneisses for a distance of a 

 mile or more. 



The stratigraphic order of succession for the sedimentary rocks 

 is^stated by Dr Ogilvie to be hornblende gneiss at the base and 

 limestone above, with the mica schist interbedded in both. The 

 field relations do not indicate any unconformity between the differ- 

 ent members. Concerning the relative age of the eruptives, Dr 

 Ogilvie states that the anorthosite is probably the oldest while 

 the granite and syenite are nearly of the same period. The gabbro 

 was the last to be intruded. The most probable order is anortho- 

 site, syenite, granite and gabbro. 



The stratigraphic relations of the Hammondville gneiss present 

 perhaps the most difficult problem in the geology of the district 

 and one that is of special interest owing to its bearing upon the 

 magnetite deposits. The question naturally involves the origin 

 of the gneiss, whether this is to be considered a member of the 

 sedimentary series and like the other members has received its 

 crystalline character by metamorphism, or whether it represents 

 an intrusive of which the original igneous features have been 

 obscured through crushing and possibly a partial recrystallization. 

 The evidence obtained from a study of thin sections of the gneiss 

 is inconclusive. As has been previously stated the mineralogy 

 differs in some respects from that of typical igneous rocks of analo- 

 gous composition, though the differences are not so great that 

 they can be regarded as decisive. Compared with the class of 

 igneous rocks most closely allied in composition, that is the diorites, 

 the chief points of contrast are in the proportions of quartz and 

 ferromagnesian minerals, the former being much larger and the 

 latter smaller than obtain usually in diorites. To substantiate 

 these inferences chemical analyses of the gneiss are needed. 



The field observations of Mr Newman and the writer lend some 

 support to the view that the gneiss does not belong to the intrusive 

 series, or at least is not contemporary with the other members of it. 

 The granulation and intense crushing which the rock has under- 

 gone is not common in the same degree to the igneous types which 

 at most show these effects in limited areas or zones where faulting 



