148 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



i3 heavily timbered through most of its extent. Blanks- of three hundred 

 feet or more occur at several points within the section. The composition and 

 other salient features of the formation are, therefore, not known with anything 

 like the certainty that attaches to the other members of the Summit series. 



This group of sediments underlying the Wolf grit and resting on the 

 Irene volcanics, may be called the Monk formation, after the name of the creek 

 which cuts across its outcrop. The total thickness is very great; a minimum 

 of 5,500 feet is estimated. There is also considerable heterogeneity in the mass. 

 Nevertheless, it is considered advisable to group all these beds under the one 

 formation name. The definite naming of the lithological subdivisions is not 

 warranted until better exposures are found than those so far studied. 



The subdivision shown in the following columnar section is to be con- 

 sidered as decidedly crude. The thickness of seme of the members could only 

 be conjectured, since the outcrops in such cases were discontinuous and quite 

 insufficient to give assured conclusions as to the composition of the covered 

 beds. The estimates then given were partly based on the character of the 

 i wash ' and even that was often thoroughly buried under the dense forest 

 cap. When, in the future, this mass of strata is stratigraphically well worked 

 out, it will doubtless be profitable to recognize by distinctive names certain of 

 the subdivisions ; the name ' Monk formation ' may then be restricted to the 

 most important member recognized in the re-examination. The columnar section 

 for the formation may b^ tentatively described as follows : — 



Columnar section of Monk formation. 



Zones. Thickness. 



Top, conformable base of Wolf formation. 



a 120 feet. — Sericite-quartz schist. 



b 50 ii Quartz grit, little sheared. 



c 650 ii Sericite-quartz schist. 



d 20 H Coarse grit, little sheared. 



e lOOO+n Sericite-quartz schist, sometimes cyanitic. 



/ 600+M Dark gray slate and phyllite. 



g 1300+ " Chiefly sericite-quartz schist with interbeds of sheared grit and 



conglomerate ; poor exposure. 



h 550 ii Sheared quartz conglomerate. 



i 700+" Chiefly sericite-quartz schist and sheared quartzite ; poor expos- 



ure. 



j 60+n Schistose conglomerate. 



k 250 „ Phyllite. 



I 200+,, Phyllitic slate. 



5500±" 



Base, conformable top of Irene Volcanic formation. 



As a rule it is very difficult to determine the attitude of the bedding, so 

 effectually is that structure masked by the never-failing schistosity. The most 

 of the readings of true dip were obtained at the contacts of the grits and 

 conglomerates with the schists. At such points the average strike was about 

 N. 10° E. and the dip from 75° W. to 90°. The corresponding readings for 

 schistosity gave, on the average, nearly the same strike, with dip ranging from 

 79° W. to 55° E., averaging 'nearly vertical. However, at one locality the 

 bedding and schistosity of a slate-phyllite phase, though holding the regional 



