The Tripolite Deposits of Lilicur. 255 



of tripolite are to be seen turned up by the plough-share 

 from under the turf, which rests upon Silurian slate. 



The occurrence of tripolite in these two situations shows 

 that the remains of diatoms had there already accumulated 

 prior to the lava flows, while those on the high ground above 

 the Caralulup Creek were deposited subsequently. The 

 accompanying plan and section show the relative mode of 

 occurrence of the several tripolite deposits, as well as illus- 

 trate the general geological structure of the locality. 



The diatoms which make up the tripolite of Lilicur are 

 principally of the three well-known forms — Pinnularia (P. 

 viridis), Navicula, and Synedra. In addition there is a great 

 abundance of small parallel-sided and oval-ended hollow 

 bodies, which, but for the absence of the characteristic 

 longitudinal furrows, might be mistaken for Baltryllium. 

 The first three genera are denizens both of fresh and salt 

 water, and their presence would not, therefore, by itself 

 define the geological position of the deposits. Enough, how- 

 ever, has been observed and herein noted to warrant the 

 statement, on physical grounds, that the Lilicur beds are 

 fresh- water lacustrine formations of Upper Pliocene or 

 Pleistocene age. 



Ballaeat, 1st October, 1886. 



