D. B. WAED, M. D. 79 



prolonged drought, making the water brackish and 

 bringing these marine species up from the ocean. Such 

 as are capable of living in fresh water have remained and 

 propagated their kind ; those incapable have died and 

 sunk into the ooze on the bottom of the river. The ma- 

 rine species differ from those of fresh water. 



Each flora is distinct. Most of the very large and 

 showy forms are marine, although there are some ex- 

 ceptions. Some genera are exclusively marine, some 

 exclusively fresh-water, wtiile others have representa- 

 tives in both salt and fresh water. It would be quite im- 

 possible, even after years of observation, I think, to 

 catalogue all the diatoms found here so as to make the 

 list complete, on account of the occasional presence of 

 stray forms. Indeed I would not be surprised to find 

 here any of the species found on the Atlantic coast, and 

 we would naturally expect in so large a body of water 

 fed by so many streams from the east, west and north, a 

 great number of fresh-water species, and such is the fact, 

 and even with these there is the same difficulty of stray 

 visitors as with the marine forms. For example, from a 

 collection made at Mine Point I found a minute diatom 

 which was a stranger to me, and for which I could not 

 for a long time find any name, and in the mean time I 

 lost the diatom although I had a good photograph of it. 

 I searched through the same material, looking over hun- 

 dreds of thousands of diatoms, and failed to find a single 

 valve like the one I lost. Some time after I chanced to 

 run across hundreds of them in a fossil deposit from 

 Canada. The gentleman who sent me this material was 

 familiar with the form and I have found that it is quite 

 common in some places. I can testify that it is not com- 

 mon here. It is called achnanthidium tiexellum. It is 

 only about 4 of an inch long, and it seemed a waste of 

 time to take so much pains with so insignificant a speci- 

 men, but I have found it will not do to despise a diatom 



17 



