1899] MICROSCOPICAL JOURNAL 51 



being left. This semi-crystaline mass effervesces and 

 therefore seemed to be a carbonate of lime and hence the 

 reason for supposing the marl to be chalky and therefore 

 cretaceous. But when examined by means of the micro- 

 scope, it is not amorphous (as chalk is) but is mineral and 

 called Thinolite by Clarance King in 1878. The name 

 Lahontan was given by him to a great Quaternary Lake 

 in Northwestern Nevada, of which the present Walker, 

 Carson, Humboldt, Winnemucca, Pyramid and Honey 

 lakes are the relics. 



The water of Lahontan Lake was fresh, but, as it 

 evaporated, the water itself went off and the solid matter 

 was left. This resulted in the precipitation of the matter 

 which was called calCKreous tuffa. When examined 

 chemically, it is found ty be not calcareous alone but a 

 compound of carbonates of \ime and magnesia, and oxides 

 of iron and alumina, along with phosphoric acid. The 

 mineral Thinolite (from the (^ reek for shore since it forms 

 on the shores of the lake),^ When the Thinolite is acted 

 upon by nitric or hydrochloric acids the lime and mag- 

 nesia are dissolved and the Diatoms, which consist of 

 opal, a hydrate of silica, are left, and they can be exam- 

 ined. They are found to be the following : 



Cymbella cistula, H. ; C. lanceolatum, C. G. E. 



Fragilaria construens, C. G. E. 



Gomphonema affine, F. T. K. 



Melosira distans, F. T. K. Common. 



Navicula firma, F. T. K. ; N. (formosa ?) var. libur- 

 nica, A. G.; N. placentula, C. G. E.; N. sphaero- 

 phora,F. T. K.; N. viridis, F. T. K. Common. 



Nitzschia spectabilis, (E.) J. R. 



Stauroneis phoenicentcron, C. G. E. 



Synedra ulna, P. A. C. N. 



Tetracyclus lacustris, J. R. Common. 



Sponge spicules probably from Spongia fluviatilis, L. 



Shells of Hyalosphenia cuneata, F. S. — chitinous. 



