1815.] Transactions of the Geological Society, Vol. IL. 61 
transition lime-stone, as lucullite has only been hitherto observed 
in that position. 
Our author gives a description of the lime-stone of Isla, and 
says it is the general opinion of the Scotch mineralogists that it is a 
floetz lime-stone. This is surely a mistake. Mr. Jameson, in his 
Travels, calls it primitive lime-stone ; and as far as my information 
goes, this is the general opinion at Edinburgh. How far it is cor- 
rect, I have no means of knowing, as I never visited the island. 
The craig of Ailsa is a well-known mountain, that rises out of the 
sea at the mouth of the Frith of Clyde. Dr. M. rightly calls it a 
syenite. From its texture and resemblance to the syenite of Arran 
there can be little doubt that it is a floetz syenite. The rock of 
Syene is a true syenite. It does not occasionally contain hornblende; 
that mineral is an essential constituent. Syenite is connected usually 
with porphyry, not with granite ; primitive syenite with primitive 
porphyry ; and floetz syenite with floetz porphyry. Hence the 
propriety of giving the same name to both ; and hence the reason 
for separating the rock from granite, with which it is not con- 
nected. 
An account is given of Devar, an island at the harbour of Camp- 
bellton, composed of felspar-porphyry. Dr. M. says this rock 
constitutes the finest specimen of porphyry he has seen in Scotland. 
Much finer, however, exist in Arran. Our author’s invectives 
against the word porphyry are very amusing. 1 am not aware that 
any ambiguity exists in the use of that term. Porphyry is a rock 
consisting of a basis containing crystals of felspar imbedded in it. 
These crystals are essential to the stone, and therefore never want- 
ing. The term porphyry, like trap, is generic. The speeies are 
distinguished by naming the base, and prefixing it to the term por- 
phyry. Thus felspar-porphyry, clay-stone-porphyry, horn-stone- 
porphyry, pitch-stone-porphyry. There is no ambiguity here. 
Every mineralogist knows, or ought to know, that these bases are 
connected together, and pass into each other. If I am told that a 
rock is composed of porphyry, I ask what porphyry? The answer, 
felspar-porphyry or clay-stone-porphyry, defines the species. It is 
true that porphyry occurs in different formations; so do trap and 
lime-stone ; but it will be found that it assumes a similar position in 
all the different formations. 
Under the head Arran, Dr. M. introduces a discussion whether 
granite ever occurs stratified or not, and terminates as follows:— 
“ We have, however, a perfect certainty that it (Arran granite) is 
not stratified, because veins are found arising from it, and entering 
the mass of incumbent schistus in the well-known junction at Loch 
Ranza.” 1 do not perceive the force of this mode of reasoning. Dr. 
M., I dare say, will admit sand-stone to be a stratified rock ; yet 
veins of it passing into the incumbent rock are not uncommon in 
quarries near Edinburgh. 
Under the head of Portsoy, Dr. M, enters into some speculations 
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