DRAINAGE OF SECRET CANYON. 109 



firms this fact by the finding of a group of Silurian fossils which are 

 characteristic of the upper beds of the horizon. Among the species found 

 here on the north base of the Peak are Ortiiis perveta, 0. tricenaria, Itaphis- 

 toma nasoni, and Eeceptaculites mammillaris. The Prospect Mountain lime- 

 stone follows around on the south side of Surprise Peak, thence southward 

 until lost beneath the extravasated lavas, which encircle the ridge where it 

 falls away toward Fish Creek valley. From Surprise Peak southward 

 these limestones lie unconformably against Pogonip beds, the former stand- 

 ing at the usual high angles of 60 or more, and the latter also dipping 

 eastward, but at angles varying from 35 to 45. 



secret Canyon. This canyon forms one of the most prominent physical 

 features of the district, a deeply eroded valley lying between two parallel 

 ridges, one of Prospect Mountain limestone and the other of Hamburg 

 limestone. The canyon lends its name to the intermediate body of argil- 

 laceous shales which are better exposed here than elsewhere. For more 

 than 2 miles in length the narrow valley is cut out of these easily eroded 

 beds, the harder limestones rising upon each side in abrupt walls several 

 hundred feet in height. There are few finer instances to be found any- 

 where of a valley carved out of soft friable material, the beds of which 

 lie highly inclined and conformable with overlying and underlying strata 

 of superior hardness, withstanding erosion better. No one overlooking 

 Secret Canyon from any high point in the country would understand the 

 appropriateness of the appellation; its true significance is recognized only 

 when approached from the south. The course of the present drainage 

 channel follows the trend of the shales until nearly opposite the southern 

 end oi Roundtop Peak, when, instead of maintaining its direction along 

 the line of the shales for a short distance further and thence out through 

 the Quaternary covered slopes to Fish Creek valley, it turns suddenly, fol- 

 lows a narrow defile obliquely through the ridge of Hamburg limestone and 

 shale, carves its way through the Pogonip and Eureka quartzite, cn> 

 the Hoosac fault, and is again deflected to the south only by Carbon Ridge. 

 The reason for its leaving the valley of Secret Canyon is to be found in 

 the rhyolite mass which probably underlies the hills of detritus near the 

 entrance to the canyon, blocking the former drainage channel. This is, 



