NOTICE. 
(TO PRECEDE THE FOURTH EDITION OF ' SILURIA.') 
The reader of this edition will find that a very important change has been 
made in my views as given in former editions, respecting the age of the 
Upper Sandstones of Elgin and Boss-shire, which I have hitherto classed 
with the Devonian or Old Red Sandstone. My previous conclusion was 
founded entirely on the strong natural evidence presented, to me, by the 
conformable superposition of those beds to the strata of the inferior and 
unequivocal Old lied Sandstone replete with its well-known fossils. This 
opinion was confirmed by the examination of the rocks in question by 
Professor Eamsay, Professor Harkness, the Eev. George Gordon, the Eev. 
J. M. Joass and others. 
The existence, in strata of Devonian age, of reptiles of so high a class as 
the Telerpeton (see fig. 73 in my last edition, p. 289) and the Stagonolepis 
was not, indeed, admitted by me without great reluctance, inasmuch 
as, if eventually substantiated, it would have weakened the main argu- 
ment that runs through all my writings, which shows a regular pro- 
gression from lower to higher grades of animals, in ascending from the 
older to the younger formations. Most joyfully, therefore, did I welcome 
the remarkable identification by Professor Huxley of the Hyperodapedon 
of the New Eed Sandstone of Warwickshire with the Hyperodapedon of 
Elgin ; and bowing, as I have always done, to clear palaeontological proof 
I have now excluded all that portion of my former editions which placed 
these reptiles in the Old Eed Sandstone. 
The importance of this rectification, due to my eminent associate, has 
very recently received a wide extension ; for among the fossil remains 
collected in India by the late Eev. S. Hislop, Professor Huxley has also 
found the Hyperodapedon. 
The formation in India containing this reptile has been considered by 
Professor Oldham, the Director of the Indian Geological Survey, to be 
either the Trias (New Eed Sandstone) or the representative of an intermede 
between the Palaeozoic and Mesozoic rocks. In all probability this cor- 
relation will have to be extended to South Africa, since one of the 
characteristic fossil reptiles of that country, the Dicynodon, has been found 
in the Eanigunj beds of this age in India. 
I take this opportunity of further stating that I have not adverted in 
the Preface to a great number of important additions which I have made in 
this edition ; they are, in fact, so numerous that, if a smaller type had not 
been used, the work would have been swollen to an unreadable size. 
EODEEICK I. MUECHISON. 
Oct. 30, 1867. 
