482 H. p. GUSHING ASYMMETRIC DIFFERENTIATION IN SYENITE 



seem well demonstrated, especially when it is considered that we are 

 dealing with the contact between two bathyliths of contrasted eruptive 

 rocks, and that one of them, near the contact, is full of dikes of a rock 

 similar to the other and with dikes of no other kind, while the reverse 

 is not the case, but instead occasional inclusions of anorthosite are found 

 in the syenite. 



Soaked Anorthosite 



In the area along the north border of the map, and also farther north 

 on the next map sheet (Saint Eegis quadrangle), are a few exposures 

 of a type of a rock which seems most expressively described as anortho- 

 site soaked by syenite. This is the area just noted as lacking the ordi- 

 nary, non-porphyritic gabbro border, the rock adjacent to the syenite 

 being anorthosite gabbro, in which labradorite augen always occur, often 

 plentifully. In the soaked rock these augen are present, and in so far 

 the rock is distinctly anorthosite; but the matrix is distinctly of the 

 syenite type, having the characteristic green color of that rock and with 

 microperthite as the prevailing feldspar ; yet the proportion of plagioclase 

 is larger than in the usual syenite. Chemically also the rock is of an 

 intermediate type. It is an impossible matter to tell how much of the 

 granular portion of the rock is of syenite derivation and how much came 

 from the anorthosite, since in both rocks much of the granulated feldspar 

 is unmarked, showing neither twinning nor intergrowths. 



The ferro-magnesian minerals also are very like in both rocks. It is 

 probably for this reason that the existence of soaked rocks along the con- 

 tact of the syenite and the gabbro border has not been demonstrated. 

 Both are fine grained and lack augen and resemble one another so much 

 that soaked rocks would defy recognition. 



It is, however, suggestive that, whereas usually there is little difficulty 

 in discriminating between the gabbro and the basic syenite in the field, 

 in frequent cases rocks are found which defy classification and which 

 may well be soaked rocks. The matter is much simplified so soon as 

 labradorite augen are present, and in the rock, under consideration there 

 seems no question but that the augen are of anorthosite derivation, and 

 that a respectable amount of the granular portion is syenite. 



The only outcrop of soaked rock seen from which material fresh 

 enough to repay careful study could be obtained is in a rock cut by the 

 railway nearly 5 miles north of Tupper Lake Junction, and hence be- 

 yond the map limits. The rock has numerous dark blue feldspar augen, 

 easily proved to be labradorite by the specific gravity and by the extinc- 

 tion angles shown on cleavage pieces. The remainder of the rock 



