GEOLOGY OF THE PORT LEYDEN QUADRANGLE I5 



cal rock in the Diana-Pitcairn area, the dark minerals, especially 

 pyroxene, are prominent constituents, while in the Port Leyden 

 district the pyroxene is always absent and the dark minerals 

 never amount to more than 7 or S^c. Otherwise the rocks are 

 very similar. In passing northwestward from Little Falls to 

 Port Leyden the syenite loses its pyroxene and the microperthite 

 becomes more prominent than the anorthoclase. 



It is now well established, especially by the excellent work of 

 Smyth,^ that the syenite is a plutonic igneous rock which has 

 been intruded into and is therefore younger than the Grenville. 

 The evidences from the Port Leyden region are clearl}^ in har- 

 mony with this view. Thus the Grenville area east of Fowlers- 

 ville is surrounded by pure syenite and the writer is convinced 

 that we have here a good example of a large Grenville inclusion 

 in the syenite. Significant in this connection is the fact that 

 the strike of the foliation in the Grenville is north and south 

 while that of the nearby syenite is about n. 30° e. This would 

 be expected especially where large sedimentary masses were 

 caught up in the molten syenite. Near Lyonsdale, on the south 

 side of the river, the syenite and Grenville are in sharp contact 

 while north of the river they appear to blend into each other. 

 Around Kosterville no sharp contacts are seen but the syenite 

 and Grenville seem to be mixed around the borders of the Gren- 

 ville. Referring to similar phenomena farther northward Smyth^ 

 says : " Some of these inclusions are clearly defined with sharp 

 boundaries but others are somewhat blended with the surround- 

 ing syenite as though they had rmdergone a partial melting." 

 The small basic inclusions above mentioned and the very inti- 

 mate mixture of syenite and Grenville on a large scale as de- 

 scribed below also argue for the intrusive character of the 

 syenite. 



Granitic syenite gneiss 



In the northern portion of the quadrangle, and on either side 

 of Black river, two areas of granitic syenite gneiss are shown 

 on the geologic map. These areas are probably continuous 

 under the broad drift-filled valley bottom. This rock is almost 

 certainly a granitic phase of the normal syenite above described, 

 and, since the one rock grades into the other, the drawing of a 

 boundary line must of necessity be an arbitrary matter. In 



^loc. cit. 



*loc. cit. p. 477. ' 



