Magento add CMS Static Block underneath categories in left sidebar

Paste below xml code in custom design part  for call static block after left navigation.

 <reference name="left">
<block type="cms/block" name="book_left_block" after="catalog.leftnav">
<action method="setBlockId"><block_id>book_left_block</block_id></action>
</block>
</reference>

For remove left navigation from left sidebar.
 <reference name="left">
<block type="cms/block" name="book_left_block" after="catalog.leftnav">
<action method="setBlockId"><block_id>book_left_block</block_id></action>
</block>
<remove name="catalog.leftnav" />
</reference>