I Regret that in consequence of the omission of a correction in my letter (GEOL. MAG. Dec. 1881), I represented Dr. Callaway as stating that the Nebo rock was granitoidite instead of a part of the granitoidite series. When the letter was written, I was not able to refer to Dr. Callaway's paper for his exact words, and on seeing the paper two or three days later, and finding that I had not given accurately the words, I wrote at once to the Editor of the GEOLOGICAL MAGAZINE, asking him to substitute for the word “granitoidite” the words “Pre-Cambrian rock.” By inadvertence this was not done, and as proofs of letters are not usually sent to authors for correction, I found that the alteration had not been made when the December Magazine appeared.