92 MEMORANDA. 



nately the precise locality is mentioned for but two of the spe- 

 cimens. I will designate them as specimens A, B, C, and D. 



Specimen A. — This is a very light white substance, made 

 up of the siliceous shells of fluviatile Diatoms. The predo- 

 minant species are a small Gallionella and a Discojdea, mingled 

 with a few species of Ejnthemia, Cocconema, Gomphojiema, 

 and Spotigiolites. This specimen was without a label, but is 

 believed to be the specimen referred to in the following 

 extract from a letter received from Lieut. Williamson : — " You 

 will find some of the light white clay from Pit River, which 

 I spoke of to you." This is, I believe, the same substance 

 which has given rise to the newspaper accounts of cliffs in 

 California composed of carbonate of magnesia. 



Specimen B. — This is a light white chalky mass, whose 

 locality is not given. It consists of fluviatile species, among 

 which various species of BiblaTiiim are quite abundant. The 

 species of this genus have been found living in Siberia, and 

 fossil in Oregon. Lieut. Williamson's specimen resembles 

 the Oregon mass found by the U. S. Exploring Expedition 

 under Captain Wilkes, but presents a different group of forms 

 and therefore must be from a different locality. 



Specimen C. — This is also a chalk-like mass, whose precise 

 locality is not marked. It is composed chiefly of a minute 

 species of Gallionella, mingled with sieve-like discs, which at 

 first would be referred to the marine genus Coscinodiscus ; but 

 the entire absence of all other marine forms, and the presence 

 of several decidedly fluviatile species, make me believe that 

 the deposit is a fresh-water one, and careful examination of 

 these discs show that they are more nearly allied to the fresh- 

 water genus Stephanodiscus than to the marine Coscinodiscus. 



Specimen D. — Is an ash-coloured earth, marked as from 

 near the Boiling Spring, Pit River. It is chiefly remarkable 

 for containing a great number of Pkytolitharia, or remains of 

 the siliceous portions of plants, mingled however with nu- 

 merous minute fluviatile Diatoms. 



It is hoped that travellers in California and Oregon will 

 keep a look-out for specimens of light white clay-like sub- 

 stances, and carefully marking the locality at the time of collec- 

 tion, send them to me for microscopic examination. Even a 

 minute portion sent by mail will be very acceptable. — 

 J. W. Bailey. — American Journal of Sciences. 



I»owcIl ami Kienland's IVcw Condenser. — In the last October 



number of the ' Microscopical Journal,' I observed a notice 

 of Powell and Lealand's new condenser, by Dr. Inman of 

 Liverpool, in which he mentions his having demonstrated the 



