PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 517 
transition of greywacke into his syenite, the rock “ exhibiting a great quantity 
of micaceous scales,’"—remarking : ‘‘ We can only recognise it as a peculiar 
yariety connecting it with more crystalline strata, and ably supporting the 
propriety of retaining the term ‘Transition Series’ as expressing a group of 
which greywacke is the characteristic type.” 
At page 493 he considers its relation to serpentine, remarking: ‘ From the 
district round Portsoy the examiner may soon assure himself that the serpen- 
tine presents characters which, when conjoined with those of the syenite, 
indicate that both form parts of a mass which has been the product of one 
epoch, and the elaboration of one great system of causes. Whenever the two 
rocks meet each other, and there are no instances in which they are far distant, 
there is an intermixture so gradual, that whatever their mode of formation has 
been, we can only consider the one as a variety of the other.” DE LA BECHE is 
quoted as saying of the rocks towards Roscreage Beacon, Cornwall: ‘ Well 
characterised hornblende slate is found in many places near the serpentine, and 
also so mixed with ordinary greenstone rocks that to attempt a separation would 
appear a violation of natural union.”* 
Having fortified myself with the above very emphatic evidence, I shall only 
say that the extreme micaceous variety which I have described from Cowhythe 
and Craig Burn would, had I not traced as far as possible its connections, have 
been taken by me for a peculiarly granular variety of the ordinary lepidomelane 
gneiss of the district, or for a highly metamorphosed greywacke. There isa 
rock to be seen a little above the bridge at Huntley which seems to be 
the same, with merely the addition of grains of quartz and an increased 
amount of the mica: its appearance is quite that of a highly micaceous 
and laminated gneiss, and it seems to shade off into the ordnary gneiss of the 
district. 
I have not seen the transition into greywake; but, with a certain qualification 
of CUNNINGHAME’S expression, “the product of one epoch,” I maintain to the 
full the most intimate connection with serpentine. I goa step further, however, 
and say, another rock must come immediately, and, as regards Portsoy, some- 
times interstitially into the same category, namely, diallage. Diallage is here 
a quite subsidiary variety of diorite, and it is this variety which usually passes 
into serpentine. CUNNINGHAME must concede this, for he says: ‘Serpentine is 
geognostically the frequent attendant of diallage, passing into it by the most 
gradual transitions.” 
Here, then, we. have the independent evidence of three observers that, as 
matters of fact, diorite passes by “insensible gradations” into greywacke, or 
* Would it not, then, be a “ violation of natural union” to “attempt a separation” of the ten beds 
which, on the west shore of the Bay of Durn, alternate with, without once intersecting, each other ? 
VOL. XXVIII. PART II. 65 
