THE 



QUARTERLY JOURNAL 



OF THE 



GEOLOGICAL SOCIETY OF LONDON. 



EDITED BY 



THE ASSISTANT-SECEETAEY OF THE GEOLOGICAL SOCTETr. 



Quod si cui mortalium cordi et curae sit non tantum inventis haerere, atque iis uti, sed ad ulteriora 

 penetrare ; atque non disputando adversarium, sed opere naturam vincere ; denique non belle et probabiliter 

 opinari, sed certo et ostensive scire; tales, tanquam veri scientiarum filii, nobis fsi videbitur) seadjungant. 

 — Novwn Organum, Prcefatio. 



VOLUME THE FORTY-. 



1891 



LONDON : 

 LONGMANS, GREEN, AND CO. 



PARIS: FRIED. KLINCKSIECK, 11 RUE DE LILLE; F. SAVY, 2i RUE HAUTEFEUILLE, 



LEIPZIG; T. O.WEIGEL. 



SOLD ALSO AT THE APARTMENTS OF THE SOCIETY. 



MDCCCXCI, 



