Even though you have applied a black to transparent gradient, via the layer effects, to your top layer, I can see that the layer itself is still filled with white.
Set the fill of the top layer to 0%
Another tip for you: Change both colors of your gradient to black, then adjust the opacity. Leaving the gradient as a Black > White one will mean that the colors between the two points are not only black, but varying shades from black to white and therefore not a true black to transparent gradient
Here you can see what you have right now: a white layer with a black > transparent gradient style applied to it. As you can see, the fill color of the layer is still white
You need to decrease the fill of the layer to 0%, which will make the layer transparent, allowing your transparent gradient to work
A simple break-down:
- Fill is the base upon which your layer styles are applied. No matter what styles or effects you add, the fill is still underneath it all. Change this to affect only the fill of the layer and leave your styles intact
- Opacity affects the entire layer (fill and styles). Change this to decrease the opacity of everything on the layer