The River Smithford to Lyell 



object of testing the depth of the marl, the red sandstone 

 was reached at a depth of 1 50 feet, and a supply of good 

 water, sufficient for the purposes of the works, was 

 obtained from this. Other trial holes showed that the 

 marl diminished in thickness towards the north, and a 

 small cutting at x (Fig. 17) exposed the junction with 

 the underlying sandstone. Fig. 17 shows the relations 

 of the beds to one another. 



The red marl contained numerous thin layers of 

 gypsum, which is a hydrous sulphate of calcium 

 (CaSO 4 .2H 2 O), and one thick bed of the compact variety 

 known as alabaster. The marl was used for the manufac- 



FiG. 17. a, Keuper Marl ; b, Keuper Sandstone. 



ture of bricks and tiles, and the gypsum burnt to form 

 plaster of Paris, the coal for these operations being 

 mined in the neighbourhood of Lyell and brought down 

 to Red River by barges. 



The red sandstone with its overlying deposit of red 

 marl constitute the two divisions of the Keuper, the 

 upper part of the Triassic Formation, and are known as 

 the Keuper Sandstone and Keuper Marls respectively. 



While at the brickworks we were told that there was 

 a very fine waterfall on the Red River, and we decided 

 to visit this as it appeared, from the description given 

 us, to lie upon the line of the Black Point Dyke. It 

 was a good day's journey through the forest, but, as 



117 



