1897] MICROSCOPICAL JOURNAL. 175 



of selenite, and matted crystalline plates. The contents 

 of the deposit offer many points of study interest. 



With regard to the richness of the deposit, it becomes 

 only a question of concentration and cleaning as the dia- 

 toms are in illimitable numbers, a fragment as large as 

 a lima-bean yielding three or more slides of the usual 

 size. A few peculiarities to be noted by the student are 

 of the following character. The Coscinodiscoidal forms 

 range in size fron l^-SO inch to 1-500 inch. Of Melosira 

 there are simple closed rings and spiral forms of two 

 or more turns ; filaments of Melosira having as many as 

 fifteen frustules united together. The Triceratia are 

 sometimes found in filaments of three or four frustules 

 in a linear series ; spherical Coscinodiscii united in pairs 

 in a partial fission or sporangial stage. In these the 

 external hemispheres are fully completed in their reticu- 

 lar surfaces, and the internal halves either perfectly or 

 partially formed, but still enclosed by the sporangial 

 isthmus or hoop. There are Amphitetras in prefission 

 union or sporangial stage inclining the frustules to rest 

 on the longer axis. The discoidal forms of all kinds 

 have both valves united to the hoop thus enabling the 

 sculptural details of either top or bottom surfaces to be 

 examined with equal facility in focussing down from one 

 surface to the other or vice-versa. 



By this means, it is seen that in all of the Aulacodiscii 

 or Glyphodiscii having processes or bosses on both sur- 

 faces that upon focussing on the upper surfaces, and then 

 through to the lower surfaces the bosses or processes of 

 the lower surfaces bisect the position of the upper bosses. 

 This furnishes a proof that the valves are intact, a cir- 

 cumstance seldom observed in other fossil deposits. 



The formation in which this deposit is found is known 

 as gypsous in character. This is owing to the fossil 

 Foraminifera and Diatoms having been mineralized or 

 metamorphosed by two agencies. As a result this tends to 



