yeast etc... on bottom of carboy??

I'm making my first home brew as we speak. It's been fermenting for about 16 hours now. The airlock is bubbling steady, and everything looks okay, but there is a thick layer of yeast or something on the bottom of the carboy. It makes sense that the yeast would collect on the bottom, but this happened almost immediately.

I boiled two gallons of water and poured that into the carboy first, let it cool as my wort boiled, and then I poured the rehydrated yeast into the carboy 10 minutes or so before pouring the 3 gallons of wort into the carboy.

It's about two inches thick. I would assume this is yeast since I can't imagine what else it could be.

Is this something that normally happens so soon into the process? Thanks for any help.

It is normal and it is good.
The majority to start with should be the cold break. Proteins and hop residue and yeast when it's done orgying.

Collectively it's known as Trub.
Rhymes with Pub here and Lube there.
Short for "trubaceous matter"

Great. Thanks.

As a warning... in the future you shouldn't pour boiling water into the carboy, this could crack it. You'll want to have that water ready beforehand, most people just use store-bought gallons, you could also pre-boil and cool. It is helpful to have this water near freezing so that you can drop the temp of your wort quickly.

great tip, thanks.