  We discuss the correspondence between degenerate fields of the W_N algebra
and punctures of Gaiotto's description of the Seiberg-Witten curve of N=2
superconformal gauge theories. Namely, we find that the type of degenerate
fields of the W_N algebra, with null states at level one, is classified by
Young diagrams with N boxes, and that the singular behavior of the
Seiberg-Witten curve near the puncture agrees with that of W_N generators. We
also find how to translate mass parameters of the gauge theory to the momenta
of the Toda theory.
