GEOLOGY OF THE NORTHERN ADIRONDACK REGION 325 



a precisely similar red gneiss that is found showing the intrusive 

 contacts against the anorthosite outlier in Litchfield park, and 

 which is regarded as an unquestionable phase of the syenite. The 

 rock here however is not so mashed as at Little Falls, many 

 augen remaining which are only partially granulated. The color 

 change makes it an easy matter to determine just how much 

 granular material has been produced from the crushing of each 

 large feldspar, and the whole forms a very striking and instruc- 

 tive rock. 



Amount of differentiation of the syenite. The field evidence, 

 both at Diana and at Tupper lake, seems conclusive that the 

 syenite varies into a quite basic, gabbroic-appearing rock on the 

 one hand and into red, granitic gneisses on the other, showing 

 thus considerably more differentiation in place than the anortho- 

 sites exhibit. The writer is also of the opinion that certain mag- 

 netite deposits of the region have originated as extra basic 

 segregations from the syenite magma, in strict parallelism with 

 the similar development of the titaniferous magnetite ore bodies 

 of the anorthosite. He has however yet to meet with a case where 

 the evidence for this is decisive, so that there is no intention here 

 to emphasize this view unduly. 



It is not yet clear whether the differentiation shown by the 

 syenite is wholly due to changes in the rock mass itself during 

 cooling, after the ordinary manner of such changes in igneous 

 rocks, or whether it is in part due to the incorporation in the 

 igneous mass of material melted away from the inclosing rocks. 

 If the latter process ever takes place on a large scale, we might 

 €xpect to find it here, in connection with these very large, and 

 Tery deep seated igneous masses. The general sharp and clear- 

 cut character of the contacts between the intrusives and the 

 various rocks which they cut, as well as the corresponding sharp- 

 ness of the contacts against the various inclusions of these rocks 

 in the intrusives, does not seem indicative of any incorporation. 

 ^or does the character of the border portion of the intrusive mass 

 •vary from place to place, as it successively cuts rocks of different 

 character, as would naturally be expected on this view. Yet it is 

 diflScult to bring certain features in harmony with the other view. 

 'The usual result of differentiation is to produce a rudely radial 



