INTRODUCTION. Ixxxili 
they could be altogether unknown to the author of “Siluria” in 1854? If they were 
known, he had unquestionably no right to publish such a sentence as the one last quoted. 
The Silurian key did not help us to unlock a single geological mystery in the north of 
England: and when he concludes (p. 148) that my recent observations prove that the 
Coniston grits are the equivalents of the Caradoc sandstone, he misrepresents me; and 
states, unconsciously, what is contrary to fact. What I do now state is, that the Coniston 
grits are probably the equivalents of May Hill Sandstone; because they are the mechanical 
deposits which mark a great physical, as well as a great paleontological, change*. 
(2) The next and concluding extract (“Siluria,” p. 147,) is as follows. “All we can 
safely say is, that, reasoning from the Graptolites, the whole (Skiddaw Slate) is a Lower 
Silurian Series, which is metamorphosed and obscured by igneous irruptions in its lower 
parts, and exhibits beneath it no clear representative whatever of the Longmynd or 
bottom rocks.” 
I protest against this kind of writing, and this kind of reasoning from a single fossil 
genus. The great group to which I have given (after my friend Mr Jonathan Otley) the 
name of Skiddaw Slate, is of vast thickness and great complexity of structure; and it 
certainly admits of three or four good physical subdivisions. It rises into some of the 
highest Cumbrian mountains; and is, I believe, the most ancient, certainly is one of the 
most remarkable of the physical groups of our older Paleozoic Series. If we succumb 
to the Silurian syllogism (supra, p. lvi.) there is an end of all debate. Est Jupiter 
quodcunque vides, is a dogma which shews us a royal road to a grand conclusion of 
nomenclature. The Skiddaw Slate contains Graptolites; therefore the Skiddaw Slate is 
“a Lower Silurian Series!” 
To describe the Skiddaw Slate in full detail would require a paper as long as this 
Introduction: but I may subjoin, in this place, a few facts in addition to those given in 
the Tabular View (supra, p. xxi.) 
(1) Immediately over the central Granite of Skiddaw Forest we have a very compli- 
cated metamorphic group, superior perhaps in importance to any other metamorphic group 
in South Britain. It has mineral veins which, though apparently of a much older epoch, 
present very interesting analogies to the mineral veins of Cornwall. This subgroup passes, 
almost insensibly, into the ordinary lower Skiddaw Slate, through the intervention of a 
chiastolite rock, and a porphyritic chiastolite Slate. In this respect, also, it presents 
good analogies to certain rare metamorphic rocks of Cornwall: but in that county, schorl, 
rather than chiastolite, is the mineral which more frequently seems to mark the passage 
from the Granite to the Slate. 
(2) Next, in ascending order, is the Lower Skiddaw Slate. It is of various colours; 
* Thus it is stated above (p. xxii), that if all the Cumbrian fossils below the Coniston grits, and all the fossils in and 
above the same grits (to the Upper Ludlow rocks inclusive) be formed into two groups, the two groups thus formed 
do not contain much more than three per cent. of common species. 
[2 
