1894.] MICROSCOPICAL JOURNAL. 93 



DIATOMS. 



How to find Diatomaceous Earth.— Mr, W. A. T rry of 



Bristol, Conn., sends us the following : 



It is asked how we know when we have found Diatomaceous 

 Earth ? It is of course impossible to be absolutely certain until 

 the find has been examined under the microscope, still a collec- 

 tor of experience and good judgment will make few mistakes. 

 The fresh water deposits are a' most invariably covered by a 

 layer of muck or peat. A light colored stratum below muck 

 will be either lime, day, or diatoms, if it is not sand. Sometimes 

 all mixed. If the material dries of a light gray orash color and 

 is also light in weight, it is almost certain to be rich in diatoms. 

 If the deposit is heavy, it is mostly clay or exceedingly fine si- 

 licious dust ; it is always well to examine all such deposits under 

 the microscope, and, if not rich they may contain rare vari- 

 eties. 



The marine deposits underlying the peat of all salt marshes of 

 the Atlantic coast always contain diatoms ; in some localities 

 these are comparatively rich, and frequently contain deep water 

 forms. The diatoms are not equally distributed through these 

 deposits, but are apt to lie in thin streaks or in pockets ; and 

 strata holding shallow water forms and those containing deep 

 water kinds are sometimes in close proximity. Where ditches 

 have been dug through these marshes for drainage, material 

 containing very interesting varieties is frequently thrown up. 

 Shallow water kinds usually predominate near the surface, and 

 below are streaks of deep water forms alternating with those of 

 brackish water down to a depth of over twenty feet in many 

 places. 



On the New England coast, it is not very unusual to find 

 these deposits to be Irom thirty to fifty feet in thickness. Where 

 the deposits were laid down by strong tidal currents, few dia- 

 toms will be found. They deposit in eddies aud basins after 

 the coarse sand has been left behind. 



Thf-se hints will be sufficient to guide the efforts of persever- 

 ing and intelligent investigator-t in search of Diatom.iceous 

 Earth; but they must understand that tiresome and disagree- 

 able labor is inevitable if they would win success. At some 

 future time 1 will give more detailed instructions. 



