BY L. A. COTTON. 



811 



siderable thickness of alluvium, in some places as much as 50 feet 

 in depth. The lead runs from south to north, and only the latter 

 end is covered by basalt. 



Again, between the Star of the South Mine and Davis' block, 

 a section of the lead is to be seen, where it has been exposed by 

 mining operations. In this case, a rather unusual arrangement 

 occurs (See Text-fig. 2). The pipeclay-band, which is 3 feet 



thickness, is overlaid b} 



fine granite-sand, and 



Granite Sand 3 Fesi 



Ih Wash Boulders 3 Feet. 



in 

 a 

 rests 

 on gravels, the pebbles of 

 which have a diameter of 

 about 4 mm. This deposit 

 lies at the junction of the 

 two main streams of the Ter- 

 tiary lead, and is capped by 

 basalt. 



The fourth zone mentioned 

 — that comprising vegetable- 

 debris — is of relatively rare 

 occurrence on this field. The 

 Text-tig. 2. —Section of the Tertiary Lead most typical example is that 

 between the Star of the South Mine of the Crown Jewel Mine, 

 and Davis' Block. jjere, the vegetation, which 



has been converted into lignite, overlies the drifts, and is of con- 

 siderable extent. A tunnel was driven through the drifts for 

 more than 100 feet, and the roof of this drive was in lignite for 

 the whole distance. 



iii. Physiography. 

 In an investigation of the kind embodied in this paper, the 

 two phases which are of most physiographic interest are evolu- 

 tionary ones. The problems presented are — How has the present 

 topography been developed; and what is its relation to the pre- 

 Tertiary condition] Several elements have contributed to the 

 process, and the chief of these are as follow: (1) denudation, 

 (2) earth-movements, and (3) volcanic phenomena. 



If it were possible to replace, in its original position, the mass 

 of material removed by the agency of denudation since the 



