Ailing — Problems of Adirondack Precambrian. 5£ 



gneiss) on the Dixon-Faxon properties and at Hague is 

 a syntectic, due to the " soaking' ' of the bottom layers 

 of the old sediment by the Laurentian granite. But at 

 moderate depths a fairly clean fine-grained granite (or 

 perhaps a better term would be quartz monzonite), is 

 found. This ancient eruptive is present on the Hooper 

 property, not beneath the foot-wall, but as lit-par-lit 

 injecting and saturating the Swede Pond quartzite. Its 

 behavior in affecting one stratigraphic unit here and a 

 different one there and its entire absence in a third 

 locality, is very suggestive of the igneous nature of the 

 rock. What seems conclusive evidence, to the writer, 

 was obtained at the Sacandaga Graphite Company's 

 mine near Conklingville (Luzerne sheet) in an exposure 

 showing the later granite cutting the Laurentian. The 

 latter is a quartz monzonite, slightly garnetiferous, grad- 

 ing into a monzonite which locally has been granulated 

 into a " pulpy" rock that has a remarkable resemblance 

 to the crushed anorthosite of the central Adirondacks. 

 The writer is thus in full accord with Professor Cushing 

 in his conception of the constitution of the Adirondacks ;. 

 believing that it consists of the Grenville lying upon 

 ortho-gneiss (Laurentian) which later was invaded by 

 the anorthosite-syenite-granite-gabbro eruptives. 



The writer has observed the Laurentian soaking the 

 Grenville in many localities but this effect seems to be 

 limited to the siliceous members of the old sediments; 

 the Hague, the Swede Pond and the Sacandaga forma- 

 tions being peculiarly subject to its influence, while the 

 more femic rocks such as the Beech Mountain and the 

 Dresden paramphibolites apparently escaped attack. It 

 is difficult to understand why this should be so, and this 

 presents a special problem for the future. 



One of the reasons why the Laurentian quartz monzo- 

 nite has been recognized only of late is that it has been 

 folded together with the Grenville and furthermore that 

 its eruptive behavior is laccolithic rather than batho- 

 lithic. This characteristic is in an economic sense an 

 important fact not at first appreciated. The " Dixon ' r 

 schist dips southward on the Flake Graphite Company's 

 land (Saratoga sheet) into a hill. The summit of this 

 elevation is composed of granite. In the field it was not 

 readily decided which granite it was. Petrographically 

 it proved to be a quartz-microperthite-syenite, inter- 



