GEOLOGY OF THE LONG LAKE QUADRANGLE 479 



feature of that rock. The syenite presents a sharp contrast in 

 this respect, in that its differentiation is prominently asymmetric, 

 and that, in the case of the Tupper syenite at least, this seems 

 conditioned on the nature of the bordering rock. The most of the 

 basic syenite, and all of the more gabbroic of it is in close asso- 

 ciation with the anorthosite gabbro border; and the same feature 

 is noted around the large anorthosite inclosures in the syenite. 

 It is also true of the syenite bordering the anorthosite outlier 

 in Litchfield park, this being the only basic syenite which occurs 

 anywhere in the vicinity, so that its presence is especially sig- 

 nificant. The differentiation into granite takes place on the south 

 side of the mass, the bordering rock on the south being granitic 

 Long lake gneiss. In each case the syenite grades into a rock 

 approaching in character the adjacent rock. Now the syenite is 

 unquestionably younger than the anorthosite, as will be immedi- 

 ately shown, and the observed relations seem to point to the 

 conclusion that the change is due to the actual digestion, by the 

 molten syenite, of material from the adjacent gabbro. The rela- 

 tions on the other side are not so clear, since the age 

 of the bordering granitic gneiss there is unknown. If it be an 

 older rock, as it is tentatively held to be, then the asymmetry 

 of the syenite is certain. But if it should prove to be a younger 

 granite then the view may be legitimately held that this granite 

 has cut away a large part of the original syenite mass, thus account- 

 ing for its apparent asymmetry. In consideration of the great 

 amount of syenite that must be regarded as having disappeared 

 on this hypothesis, however, it is vastly less probable than the 

 other. In this connection it should be recalled that the Diana 

 syenite, as described by Smyth, shows a quite similar asymmetric 

 differentiation.^ The character of the differentiation may thus 

 be regarded as reasonably certain. The explanation to account 

 for it, namely the incorporation of material from the adjoining 

 rocks, is much more open to question. 



The syenite younger than the anorthosite. Reconnaissance work 

 in this district in previous years had led the writer to believe 

 the syenite to be younger than the anorthosite and the evidence 

 then obtained was set forth. ^ It was not however demonstrative, 

 and as the matter is one of considerable importance in Adirondack 

 Precambric geology, it was hoped that a detailed survey of the 



I N. Y. State Geol. 17th An. Rep't. 1897. p, 471-86. 

 a Ni Y% State Geol. aoth An. Ri^p^t, 1900, p, r4i-$3.. 



