The normal "read more" code for Genesis does not add the read more link to short manual excerpts. The blow code will do so.

read-more-functions.php

<?php
// Do not copy opening PHP tag

// Add Read More button to blog page and archives
add_filter( 'get_the_content_more_link', 'wsm_add_excerpt_more' );
add_filter( 'the_content_more_link', 'wsm_add_excerpt_more' );
function wsm_add_excerpt_more( $more ) {
    return '<span class="more-link"><a href="' . get_permalink() . '" rel="nofollow">' . __( 'Read More', 'wsm' ) . '</a></span>';
}
add_filter( 'the_excerpt', 'wsm_add_short_excerpt_more' );
function wsm_add_short_excerpt_more( $output ) {
	global $post;
    return $output . ' <span class="more-link"><a href="' . get_permalink() . '" rel="nofollow">' . __( 'Read More', 'wsm' ) . '</a></span>';
}