Discontinuities may also remain unnamed as in the following example from IASP91:
77.500 8.04500 4.48500 -1.00000 -1.00000 -1.00000 120.000 8.05000 4.50000 -1.00000 -1.00000 -1.00000 165.000 8.17500 4.50900 -1.00000 -1.00000 -1.00000 210.000 8.30000 4.51800 -1.00000 -1.00000 -1.00000 210.000 8.30000 4.52200 -1.00000 -1.00000 -1.00000 260.000 8.48250 4.60900 -1.00000 -1.00000 -1.00000 310.000 8.66500 4.69600 -1.00000 -1.00000 -1.00000
The discontinuity at 210km depth will be ignored in the sense that no special treatment of it is possible. Its depth is not stored within the .dz-field of the model-structure.