out of 24 sources lie above $A_V$=15.0 mag. The fraction of the total of Class I sources, $N(>A_V)/N_{total}$, decreases steeply after that, with only 50 percent of the total number of sources remaining at levels above $A_V$=22.0 mag. It is also important to notice that given the filamentary morphology of the IRDC, the projected area of the map contained above each level decreases very steeply for $A_V>12.0$ mag. We also found that the surface density of Class I sources, $\Sigma_*(>A_V)$, defined as the number of sources divided by the area above a given level, deviates little from a power-law behavior with a slope $\beta \approx 2.9$ in the range $12<A_V<40.0$ mag. All of this is very consistent with a Schmidt type relation like it was found for a set of nearby Giant Molecular Clouds by @Lada:2013aa, except that in those clouds the linear regime appears to be set at a lower extinction interval. Unfortunately, our numbers are too small to attempt a Bayesian analysis like that of @Lada:2013aa, and possibly a comparison with other regions containing IRDCs would be more fair. However, the fact that we find a possible Schmidt-like behavior in a region like Cygnus-X DR15 is very interesting 