How to find the volume of a surface matrix from another surface matrix as a reference?

So I have two matrices in matlab which each give a seperate 3D surface plot when using mesh. For my research project I need to find the volume in between the two matrices. I've tried to use cumtrapz which I thought may give me a commulative trapezoidal volume of each then subtract. However there are two issues for this code. 1. is that it only uses a vector as a reference and 2. if a vector is used it gives me the volume in a matrix. I need one single volume solution for each matrix then subtract or find a code which uses one of them as a reference and finds the volume in between the two matrices. Any suggestions?

[Walter Roberson]

Are the two surface plots made with the same x and y coordinates?