java.lang.IllegalStateException: Detected both log4j-over-slf4j.jar AND slf4j-log4j12.jar on the class pat

java.lang.IllegalStateException: Detected both log4j-over-slf4j.jar AND
slf4j-log4j12.jar on the class pat

Can anyone tell me the difference between slf4j-log4j and
log4j-over-slf4j? Which is more standard to use in a Java web application?
I currently have both on the classpath and that is causing a runtime
exception as the web server is trying to prevent a StackOverFlowException
from happening.
Exception:
java.lang.IllegalStateException: Detected both log4j-over-slf4j.jar AND
slf4j-log4j12.jar on the class path