contour of a layer

I need to make a contour map of a reservoir layer in a subsurface. My x-range is from 35 to 48 and my y-range is from 74 to 85. They have only given me the depth of about half of the points. I'm trying to make a contour map of the layer but it won't work because it won't interpolate at the points that I'm missing. I have made a matrix of all the points but now it has a lot of NaN values. Is there a function that interpolates automatically, or do I need to use a different method? Please help.