As in the last memoir printed in the preceding number of this Journal my old friend Professor Sedgwick has animadverted upon some of my proceedings in establishing the Silurian System and in afterwards extending its application to British tracts beyond those in which it was originally formed,—I now offer, with the permission of the Council, a reply, which shall be very brief, and which, in vindicating my scientific credit, will be little more than a reference to documents published in successive years on this subject. Being perfectly sure that, whatever may have been the strength and pungency of his expressions. Professor Sedgwick had no intention to hurt my feelings, I am also certain, that he will be pleased that I thus have an opportunity of explaining what I consider to be the history of the origin and final establishment of my own Silurian classification.