title: ggplot doesn't plot two geom in one figure R
body: <p>I try to plot both <code>geom_histogram</code> and <code>geom_density</code> in one figure. When I plot the two separate from each other I get for each the output I want (histogram and density plot) but when I try combining them, only the histogram is showed (regardless of which order of the histogram/density in the code). </p>
  
  <p>My code looks like this: </p>
  
  <pre><code>ggplot(data=Stack_time, aes(x=values))+geom_density(alpha=0.2, fill="#FF6666")+
    geom_histogram(binwidth = 50, colour="black", fill="#009454")
  </code></pre>
  
  <p>I do not receive any error message, but the <code>geom_density</code> is never shown in combination with the <code>geom_histogram</code>.</p>