[R] question

[Fuensanta Saura Igual]

Does anyone know how I can read from a .txt file the lines that are between
two strings whose location is unknown?

My problem is that I have a .txt file with data separated by a sentence,
for example:

2.22 3.45
1.56 2.31
pattern 1
4.67 7.91
3.34 2.15
5.32 3.88
pattern 2
...

I do not know the number of lines where these separating sentences are located,
because the number of lines in between them can be random. If it was fixed, I 
think I could use "read.table" using the option "skip", but in this case, I do 
not know how I could manage to do that automatically.

Thanks.