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Vol. VII. DETROIT, MARCH, 1887. No. 3 



ORIGINAL COMMUNICATIONS. 



NEW DIATOM ACEOUS DEPOSITS.* 



THOS. CHRISTIAN. 



IN 1885, I had given me about one pound of what at first sight I 

 took to be a fine sand, but which the giver, Rev. Mr. Sturgis, said 

 came from an artesian well at Cambridge, Md., some 200 feet deep, and 

 that it^contained some rare diatoms. On a casual examination, I 

 could only find about one diatom to a thousand grains of sand; but 

 as he said that he had washed some, and found a few forms, which he 

 thought were rare, though very few were perfect valves owing to the 

 destructive action of the drill. Wishing to save all the rare forms, 

 if there should be any in the five strata given me, I used only 

 distilled water and my continuous boiling apparatus, by which I can 

 boil days, weeks or months as I may wish. In this case I was from 

 September to November in getting the perfect diatoms entirely free 

 from the sand and fragments, but in a very perfect manner. 



I was well repaid for all my care and 

 time, as I now have five washings from the 

 different strata, that are said to be the rarest 

 find since the celebrated Santa Moneca was 

 sent out. Soon after the material was 

 i given me, I found a perfect and beautiful 



form of Coscinodiscus excavatus, (Grev.) 

 which differs from the one described by 

 ^ "---^M^ Greville in having four conspicuous de- 



Cos. Excavatus. var. Greville. p^essions alternating with the same number 

 of elevations ; the disk is of large size and visible to the naked eye. 



* Extract from Paper read before the Richmond Microscopical Society. 



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