Guss makes some good points caddis and stone flies look a lot a like. I'd almost guarantee that you saw either black, or even better, brown stoneflies.
The reason you don't see them "emerging" is because stoneflies unlike some of the other flies (mays, caddis, midges) crawl out of the water and up the bank to emerge. The returning adults are the only "dry" flies there is when it comes to stones. That's why when the wind blew you saw activity as the bugs had taken shelter in nearby foliage and got blown into the water, ands when it got nice and sunny they proceeded in their mating business.........I could talk this stuff for hours

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I have a great little stream is SW PA that should be cooking right now because of these stones--It's THE best fishing of the year on that creek.
Remember that when you catch one(natural fly) in your hand. Stone flies will hold their wing flat against their back/ caddis wings will look like a tent (generally).

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