BETWEEN WESTON AND MIKE FAULTS. 231 



and M-16) and other shafts, is a considerable body of compact Green 

 Porphyry, apparently part of an interbedded sheet underlying the "White 

 Limestone. This extends some distance above the bridge, but opposite the 

 Belcher tunnel the outcrops of gray limestone belonging to the Silurian 

 formation are found resting on it, dipping 12° to the northeast. In this 

 limestone can be seen the outcrop of a body of coarse-grained quartz-por- 

 ph}ry similar to the rock of the dikes. For several feet from its contact 

 the limestone seems to be hardened and silicified, with small veins of por- 

 phyry running into it. It is probably either an offshoot from one of the 

 dikes already mentioned or a separate dike. 



From the steep cliff of White Porphyr}' above the Long and Deny 

 tunnel an immense talus cone of tabular and sherdy fragments of White 

 Porphyry spreads out into the valley, so as almost to block it up and to 

 completely cover the outcrops of the Blue Limestone. At first glance it 

 would seem that this immense accumulation of debris must be due to some 

 unusual cause. As none such could be found, the great height and steep 

 slope of the ridge which is occupied by the body of White Porphyry and 

 the peculiar weathering of this particular rock, which, under the influence 

 of atmospheric agents, disintegrates very rapidly into tabular sherdy frag- 

 ments, must be considered an adequate explanation. These fragments, 

 which are very light in proportion to their superficial area, slip down rap- 

 idly under the influence of rain, snow, and frost, and soon accumulate in 

 very considerable talus cones at the foot of any steep slope whose surface is 

 largely composed of White Porphyry. Owing to the depth to which the 

 rock surface is buried under this debris, the contact has not been prospected 

 between the Long and Derry mines and the First National. 



Printer Boy Hill. — On the north side of Iowa gulch, along the south slope 

 of Printer Boy Hill, the contact of the Blue Limestone and White Porphyry 

 is well marked by a series of tunnels and shafts. The First National shaft 

 finds ore at the contact after sinking through 75 feet of White Por2)hyry. 

 The Seek-no -further (E-38), Mammoth (E-39), and some other shafts 

 have also reached the contact through the porphyry. The Minor tunnel 

 and the upper tunnel of the Florence are at the highest part of the con- 

 tact, while the J. D. Ward shaft, on the summit of the hill, sinks 300 feet 



