The blend channel (fig. 3) works the same way in the Geology Service as it does in other placement textures. The 0-255 values are remapped to 0-1, where 0 means “use the existing world height here, 100%”, 1 means “use the (remapped) texture height here, 100%, and 0.5 means “blend the existing world height and the remapped texture height here, 50%-50%”.