56 Ailing — Problems of Adirondack Precambrian. 



ville and Algoman syenite, a clever but a questionable 

 procedure. 



North of the town of Saranac Lake the writer 13 

 encountered them in sufficient quantity in many outcrops 

 to see that they present a special problem of their own. 

 They are penetrated by granites (microscopically quartz 

 monzonites) that are tentatively regarded as Laurentian. 

 Can it be that the sedimentary portions of the Saranac 

 series are Huronian in age? The paraschists and para- 

 gneisses are hornblendic or micaceous rocks that do not 

 seem to grade into limestones or quartzites as is the 

 normal behavior of the Grenville. There are portions of 

 the Saranac series that cannot be separated into sedimen- 

 tary and igneous types, for much lit-par-lit injecting, 

 soaking, and assimilation has taken place. 



The writer made some investigation of the doubtful 

 members with the hope that they could be separated into 

 ortho- and para types. Microscopic analyses were made 

 by a modification of Rosiwal's method and the chemical 

 criteria proposed by Bastin 14 applied. As the attempt 

 was far from satisfactory he attempted to make the 

 separation by measuring the relative radioactivity. 

 Joly 15 has pointed out that as a general rule, to which 

 there are exceptions, igneous rocks are slightly more 

 radioactive than sedimentary rocks. Taking typical 

 specimens of the Grenville and of the Algoman syenite 

 it was found that such was the case. The values 

 obtained from tests made upon these Saranac rocks were 

 inconclusive for they were intermediate between the 

 other figures. Without question the electroscope the 

 writer employed was not sensitive enough to give reliable 

 results, but it is hoped that this line of attack can be 

 pushed farther ; what the results will be cannot be fore- 

 told. 



3. The Igneous Bocks. 

 The Early Metagabbro. 



The inclusions of green amphibolites 16 in the granitic 

 rocks of St. Lawrence County present a most difficult 

 problem. Cushing and Martin regard them as igneous 



13 The Geology of the Lake Clear Kegion (Portions of the Saranac and 

 St. Eegis Quadrangles) N. Y. State Mus., Bull, in press. 



14 Bastin, E. S. : Chemical Composition as a Criterion in Identifying Meta- 

 morphosed Sediments, Jour. Geol., 17, 445. 



13 Joly, John: Eadioactivity and Geology, N. Y. (Van Nostrand). 

 18 Martin, J. C. : N. Y. State Mus., Bull. 185, p. 57, 1916. 



