I have found rock at the beach for the first time?

For as long as I've been going to the beach, i don't think i have ever found rocks there. I go to Mustang Island, off of Corpus Christi at least once ervy summer. This time I went, I found TONS of little rocks tered with the bits of shells that you can find anywhere. Is there any reason for this? A few of the rocks looked like granite pieces you would find in the mountains, the others looked like sand stone, and one looked VERY weird... it was short, but very thin bumpy, kind of mangled looking, and looked like lead, but was WAY too light for it to be lead. Any help?