How copyright the lyrics alone ?

Is it reasonable to copyright the lyrics alone, and then later add the recordings - or is this not the best way to do it. Does that make it cost more money?

Here is what the law states:
"Copyright protection subsists from the time the work is created in fixed form. The copyright in the work of authorship immediately becomes the property of the author who created the work. Only the author or those deriving their rights through the author can rightfully claim copyright."
library

Personally speaking, I would not bother to register the lyric of a song separately from the music as I feel it is a waste of time and money.