Additional Sidebar

Your function seems fine and it’s probably hooked on init :

add_action('init','blankslate_widgets_init')
function blankslate_widgets_init() {
 //code
}

But in your theme you probably want to add some checking :

<?php if (is_active_sidebar('left-sidebar')) dynamic_sidebar('left-sidebar'); ?>

I would use left-sidebar instead left_sidebar as sidebar ID perhaps.