GLSL multitexturing

Hi experts,

I am learning shader programming, and I do not know how to place a picture on another.

My obj-c code:
[source lang="cpp"] glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, _fishTexture);
glUniform1i(_textureUniform0, 0);

glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, _floorTexture);
glUniform1i(_textureUniform1, 0);

glUniformMatrix4fv(_modelViewUniform, 1, 0, modelView.glMatrix);
glUniformMatrix3fv(_modelNormalUniform, 1, 0, modelView.glMatrix);

glViewport(0, 0, self.frame.size.width, self.frame.size.height);

glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);

glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE,
sizeof(Vertex2), 0);
glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE,
sizeof(Vertex2), (GLvoid*) (sizeof(float) * 3));
glVertexAttribPointer(_normalSlot, 3, GL_FLOAT, GL_FALSE,
sizeof(Vertex2), (GLvoid*) (sizeof(float) * 7));
glVertexAttribPointer(_texCoordSlot, 2, GL_FLOAT, GL_FALSE,
sizeof(Vertex), (GLvoid*) (sizeof(float) * 10));[/source]

And my fragment shader:
[source lang="cpp"]varying lowp vec4 DestinationColor;

varying lowp vec2 TexCoordOut;
uniform sampler2D Texture0,Texture1;

void main(void)
{
gl_FragColor = mix(texture2D(Texture0,TexCoordOut),texture2D(Texture1, TexCoordOut),1);
}[/source]

Also I have the right declarations and syntax. But it displays only one of my pictures. (I have a neon green and a grey plain texture, and the grey is shown always, no matter the query...)

As far as I know the mix() function return value is computed as follows: x*(1-a)+y*a. So if I set it to 1, the second texture (Texture1) will be above the first. I do not want to calculate some colors, I want to use the images as they are, but on top of each other.

Thanx in advance!