This is from Chicago, Lake Michigan, 1880. Both species blooming in early March. I probably need to read a bit more to understand the bloom of each species in different regions better. Sunday it is.
In the meantime, I still haven't seen anything to convince me the diatom colony in between bills had to have been alive when it got wedged there. It's dead right now and it's still together. It could dislodge and get lodged again elsewhere, so what makes the cash so special that it can only be visited by live diatoms? The money *was* partially petrified with silt, no? Also, could it have grown there, right between those two bill fragments? Could the river have seeded the beach with diatoms and the March/July blooms multiplied them in place on/in the moist cash as Georger is asking?
I think all we need is probably already written somewhere.