title: Adding minor tick marks to the x axis in ggplot2 (with no labels)
body: <p>Below is example code of a plot that does almost exactly what I want. The only thing I want to add is tick marks on the x axis (same size as the major ticks) according to the minor_breaks defined below.</p>
  <pre class="lang-r prettyprint-override"><code>df &lt;- data.frame(x = c(1900,1950,2000), y = c(50,75,60))
      
  p &lt;- ggplot(df, aes(x=x, y=y))
  p + geom_line() + 
    scale_x_continuous(minor_breaks = seq(1900,2000,by=10),
                       breaks = seq(1900,2000,by=50),
                       limits = c(1900,2000),
                       expand = c(0,0)) +
    scale_y_continuous(breaks = c(20,40,60,80),
                       limits = c(0,100)) +
    theme(legend.position=&quot;none&quot;,
          panel.background = element_blank(), 
          axis.line = element_line(color='black'),
          panel.grid.minor = element_blank())
  </code></pre>