1892.] NEW-YORK MICROSCOPICAL SOCIETY. 23 



of my subject which come naturally within the province of 

 biology, or which present themselves to the mere observer with 

 the microscope. While it is both easy and agreeable to wander 

 in the paths of speculation, we must now keep to the direct line 

 of tangible investigation, which leads us back to the consideration 

 of our little silex-coated cell and its physical substance and 

 structure. 



From what has been said concerning the architecture of the 

 typical frustule, you will have inferred that whenever, by any 

 means, its organic material is destroyed, its two valves will fall 

 apart, and that, if the diatom is in an advanced stage of incom- 

 plete subdivision, it will break up into four valves and two hoops. 

 To such constituent parts the microscopist conmonly reduces his 

 diatomaceous materiiil, by treatment with acids, for purposes of 

 permanent mounting and preservation. Nature, also, is con- 

 stantly removing the soft and perishable endochrome from dia- 

 toms which have run their life's course, and is steadily depositing 

 their nearly indestructible remains at the bottom of almost every 

 permanent body of water. As diatoms have swarmed in river^ 

 lake, and sea for countless ages, at least since the glacial epoch, 

 their flinty shells have come to form beds and strata of very con- 

 siderable extent in numerous parts of the world. Since the fresh- 

 water, salt-water, and brackish-water deposits are very dissimilar 

 in character, as are also the prevailing forms of different periods, 

 these diatomaceous (or "infusorial") earths supply chapters in 

 the history of our globe which are of very great interest and 

 importance, but which some geologist will need to expound to you. 



Amongst the largest and best-known of these deposits are that 

 which underlies the city of Richmond, Virginia, and its vicinity, 

 and the one near Virginia City, Nevada. The " Richmond 

 earth " forms a stratum of from 8 to 30 feet in thickness, lying 

 near the surface and extending throughout the eastern part of 

 Virginia and portions of Maryland. There is- some reason to 

 suppose that this extensive deposit is related to if not actually 

 connected with deposits recently discovered, at depths of several 

 hundred feet, at Atlantic City and other points in Eastern New 

 Jersey. The forms prevailing in these deposits are of the kinds 

 peculiar to salt water, and their accumulation, in these immense 

 beds of wide extent and great thickness, is evidence of a long- 



