Latest solr4 snapshot seems to be giving me a lot of unhappy logging about 'Log4j', should I be concerned?

[Benson Margulies]

CoreContainer.java, in the method 'load', finds itself calling
loader.NewInstance with an 'fname' of Log4j of the slf4j backend is
'Log4j'.

e.g.:

2012-05-01 10:40:32,367 org.apache.solr.core.CoreContainer  - Unable
to load LogWatcher
org.apache.solr.common.SolrException: Error loading class 'Log4j'

What is it actually looking for? Have I misplaced something?