What is the function of "exhausts" in this context? Does "more than exhausts" refer to "the psychic knowledge"?
Both Kate Fox Jencken and Margaret Fox-Kane died in the early 'nineties, and their end was one of sadness and gloom. The problem which they present is put fairly before the reader, avoiding the extremes of the too sensitive Spiritualist who will not face the facts, and the special-pleading sceptics who lay stress upon those parts of the narrative which suit their purpose and omit or minimize everything else. Let us see, at the cost of a break in our narrative, if any sort of explanation can be found which covers the double fact that what these sisters could do was plainly abnormal, and yet that it was, to some extent at least, under their control. It is not a simple problem, but an exceedingly deep one which exhausts, and more than exhausts, the psychic knowledge which is at this date available, and was altogether beyond the reach of the generation in which the Fox sisters were alive.