INTRODUCTION. Ixix 
ever small—it was, at least, original. I worked first, and single-handed. The only material 
changes I have made in the grouping of the Cambrian Series since 1832 have been the 
shifting of the base line of the great collective Bala group to a lower level; the adoption 
of the name Lingula flag; and the separation of the May Hill from the Caradoc Sandstone. 
In none of these changes have I owed anything to the Government Survey; and to whom 
else could I owe them*? 
4. It was hinted (and it was the only point which grieved me) that the Silurian System 
was a great work, the appearance of which made an epoch in British Palzozoic Geology; and 
that I did not treat the author with the honour and consideration he deserved. I emphatically 
deny the charge. I have done all honour to the Silurian System, and accepted its groups, and 
the names given to them, without reserve, wherever they were right and admissible. I might 
have attempted to unpack my old collection; or I might, with the utmost ease, have made a 
good new collection from the fossils of Coniston and Kirkby Moor, and submitted them to Mr 
Sowerby for determination; and thereby have endeavoured to go shares in my friend’s 
Silurian discoveries. But I made no such attempt. I was certain that his physical types 
and fossil lists were excellent, and that he had a full right to make them typical. I only 
abandoned the Silurian classification when I believed that the author had deserted his own 
principles. If I differ from a fellow-labourer, the greatest respect I can pay him is to tell 
him plainly and honestly why and where I differ from him; and it is no mark of respect to 
merge plain truth in words of stupid and unmeaning courtesy. He had made a noble conquest, 
and received from it honour enough to satisfy a reasonable ambition: but “too much honour,” 
the poet tells us, is a burden too heavy for a man to bear. My friend became ambitious 
of a more extended conquest. With much gravity he expunged his own base line of about 
200 miles in length, and then consummated what I thought an act of spoliation. If I 
resisted this, did I thereby cease to do deserved honour to the author of the Silurian System ? 
Let facts speak for themselves. He tells us, with just pride, (Siluria, p. 9) “that his 
* In three instances (and three only) I wrote for information to my friends employed on the Government Survey. 
(1) When in 1846, I had traced the Lingula flag from Tremadoe to Cader Idris, I wrote either to Mr Jukes or Mr Salter, 
and stated that if the views I had formed in 1832, of the structure of Carnarvonshire were correct, the Lingula flags 
ought to be found above the Harlech grits which overlie the great Nant Francon slate quarries. In that position I had 
sought for these flags for a few hours (during my hasty passage through the country in 1846) but had not found them. The 
reply was, that the Surveyors had found them in the position indicated. (2) I wrote some time afterwards to Mr Jukes, and 
inquired where the Llandeilo flag, of the Towy, emerged—on a line drawn from that valley to the shores of Cardigan Bay, 
or to the south-east flank of Cader Idris. The reply was, that the Surveyors considered all the rocks on those two 
lines as Llandeilo flag. When I read the reply, I must honestly state that I thought it indicated a very strange and 
unnatural nomenclature; and that it gave a very bad promise of a successful analysis of the great and difficult 
groups of South Wales. (3) I afterwards (but I have no means of fixing the date of the letter) stated to Mr Jukes— 
that if the Silurian rocks were, as a whole, unconformable to the older groups I called Cambrian, there were no 
physical difficulties in the way of a right interpretation of the whole Series—Cambrian and Silurian. He wrote in reply, 
that the hypothesis of a general discordancy had once been adopted by the Surveyors, but was abandoned. I think the 
abandonment was a great mistake. Before Mr Salter revisited the Wenlock and Horderley sections in 1853, I requested 
him to look carefully for a discordant overlap made by the true Silurian rocks. He found a discordant overlap 
which included the Norbury limestone—an important fact afterwards verified, during the same summer, by Professor 
M°Coy. By this discovery the Norbury limestone at length obtained its true place; asa part of the unconformable and 
overlying May Hill Sandstone at the physical and palzontological base of a true Silurian System. 
