Logging from web app but not external jar

[mdjj]

I've got a web app that uses commons logging and log4j. Any specific
class within the web app logs fine to my local log file defined in
log4j.properties i.e. an Action.

The web app also uses a common service layer which is defined as an
external jar.
This service layer also uses commons logging but when I try to log
anything from
a class within the service layer nothing ever gets written to the local
log files.

The web app has log4j, commons-logging in web-inf/lib as well as the
external service jar.
The log4j.properties is in web-inf/classes.

I've assumed that providing the log4j implementation through the web
app is enough or am I missing something?

I'm using Tomcat 5.5.7.