R help - May 2004 - integrate over a serie

Hi all;

I've got temporal series of data. And I'm plotting it with the type
'l', and
with a interpolating slipe.

Could you advise me about the best way  to calculate the area under any of 
these curves.  

I know it is very easy to calculate the first one, although have no idea of 
the second one. But, perhaps there is a function that I can't find to do 
directly these integration?

Thanks and best regards,

Javier