422 AV. II. TWEXHOFEL THE SILVER CITY QUARTZITES 



of the tests of FusuHna. Near Silvei- Cit}- tlie tliickness of the whole is 

 about I'Z feet. 



LE ROY SHALES 



'Hiese are of a lithologv and stratification eqaaJlY as variable as are the 

 T.awrence shales, Init in the Silver City area, they are of a lighter color: 

 red sliacles are not eommon, while yellows predominate. Ear less sand 

 is also present and the greatei- portion of the division is a shale. Small 

 flakes of mica are quite common. At the base are afjoiit 80 feet of dark 

 l)hie and black shales. The division is known to be 204 feet thick on the 

 northwestern margin of the area. 



STANTON LIMESTONES 



These are the lowest rocks exposed in the immediate vicinity of Silver 

 City. They are gray, rusty spotted limestones of variable thickness and 

 are not well l)e(l(le(l. They are not exposed in the altered area.. 



THE SILVER CITY ANTICLINE 



Tbe Silver (*ity anticline has the form of an elliptical dome with the 

 long axis trending nearly east and west. Due to lack of data, the eastern 

 margin is perhaps not qnite correctly mapped. The otlier portions of the 

 structui-e are believed to l)e fairly accni'ately drawn. AYith the exception 

 of the northeastern margin, all margins are fairly regular. The former 

 is comi^aratively irregular, and it is clear that in the development of the 

 anticline eonsideraI)le crushing and fi'acturing occurred there. There is 

 no evidence of faulting. On the conti'ary, the outcrops of the stra^ta show 

 the im])ro1)ability of the presence of a fault with a throw of more than 

 4 or 5 feet. 4'he anticline is expressed in the topogra])hy as a basin. 



Detailed Geology of Silver CrrY IJidge 



1'hc Lawrence shales and sandstojies, which on the adjacent ridges as 

 well as on the north side of Silver City ridge have the characteristics 

 ty])ical of the division, consist throughout the area in the map within the 

 heavy line of very hard, coin|)act (|uart/ites, which locally contain small 

 cavities lined with crystals of quartz and, more j'aj-ely, of pyrite. Thei-e 

 is no trace of the ]-ed colors which are characteristic of the rocks of this 

 division iu surrounding areas, but instead there . are shining gray aud 

 greenish shades. In the sunlight the quartzite sparkles brilliantly, and 

 it Avas probably this characteristic which led to its being mistaken for 

 silvei- o)-e. Examination of the i-ock in thin-sections j>i'oves it to be com- 



