This section is from the book "The Constitutional Law Of The United States", by Westel Woodbury Willoughby. Also available from Amazon: Constitutional Law.
It is not essential to due process of law that proceedings and adjudications, though admittedly of a judicial nature, should be had in courts of law. It not infrequently happens that administrative, boards or officers in the discharge of their duties are compelled to consider and decide upon matters of a judicial character, and, provided an adequate opportunity is offered to the parties to appear and defend, due process of law is not denied by making the administrative determinations they reach conclusive and not open to further consideration in the courts, except, of course, as to the matter of the jurisdiction of the officers or boards in question, or as to whether adequate notice and opportunity to defend has been given the parties affected. In short, "due process is not necessarily judicial process."26 This subject is more fully discussed in Chapter LXIV (Conclusiveness Of Administrative Determinations. 754. Due Process Of Law Does Not Deman'D Determination Of Rights In Courts Of Law) of this treatise.
24 194 U. S. 258; 24 Sup. Ct. Rep. 650; 48 L. ed. 965.
25 The court say: "We are of opinion that no federal right of the plaintiffs in error was violated by admitting this deposition in evidence. Its admission was but a slight extension of the rule of the common law, even as contended for by counsel. The extension is not of such a fundamental character as to deprive the accused of due process of law. It is neither so unreasonable nor improper as to substantially affect the rights of an accused party, or to fundamentally impair those general rights which are secured to him by the XIV Amendment. The accused has, as held by the state court in such case, been once confronted with the witness, and has had opportunity to cross-examine him, and it seems reasonable that when the State cannot procure the attendance of the witness at the trial, and he is a non-resident and is permanently beyond the jurisdiction of the State, that his deposition might be read equally as well as when his attendance could not be enforced because of death or of illness, or his evidence given by reason of insanity."