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dam (Upper Cambrian), the evidence being purely strat- 

 igraphic, for no fossils are found in this formation. These 

 sandstones are rather noted, however, for the purely con- 

 cretionery forms they contain. To the south-west of the 

 sandstone and at a higher horizon, are the Lowville lime- 

 stones (Lower Ordovician). 



As a surface covering for the whole district is the 

 usual glacial drift of Pleistocene times. This drift is quite 

 unsorted in most places over this area, but in a few localities 

 has been water-sorted into great beds of clay, sand, gravel 

 or boulders. The clays are used for the manufacture of 

 common brick and tile; the sand and gravel for building 

 purposes, road-metal or railway ballast; and the boulders 

 in some cases for building rubble masonry. Most of the 

 drift is unsorted however, so that splendid sections of glacial 

 drift, with its variety of boulders, and its erratics can be 

 obtained. 



LEAD, PHOSPHATE AND MICA DEPOSITS. 



INTRODUCTION. 



This excursion has been planned to visit a few of the 

 economic deposits found in the Pre-Cambrian rocks of 

 this district. Some of these, for example the mica deposits, 

 are amongst the largest producers in the world, and are 

 therefore interesting. Others, like the phosphate mines, 

 were formerly large producers, but are no longer worked. 

 Their association is so much like that of the phosphate 

 deposits of Norway, as described by Broegger and Reusch, 

 that they should prove interesting. The lead property is 

 not a big producer, but the occurrence is interesting in 

 that it illustrates a point in ore deposition, for where the 

 wall rocks are gneiss the ore is galena with no zinc blende, 

 but where they are crystalline limestone both galena and 

 zinc blende occur. This excursion will also afford an excel- 

 lent opportunity for studying the general character and 

 topography of a typically Pre-Cambrian area. 



