On the page http://logback.qos.ch/manual/architecture.html there the section describing SLF4J Logger API:

package org.slf4j;
public interface Logger {

// Printing methods:
public void debug(String message);
public void info(String message);
public void warn(String message);
public void error(String message);
public void fatal(String message);
}

As you see, the method names are invalid: there is no "fatal" level in SLF4J. Also "trace" is missing.