

214 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
these minerals were imbedded in the felspar, it was the residue of their separa- 
tion in the solid form. 
Orthoclase of Porphyritic Dykes. 
6. A great dyke of red porphyry crosses the Don, in Aberdeenshire, about 
half a mile north of Monnymusk, also the railway cutting to the west of 
Tillyfourie, shows itself in the pass above Greenfolds, protrudes as a huge ram- 
part for nearly two miles in the slack between the Greenhill and Corrennyhill, 
curves round at Upper Broomhill and Nether Dalgie so as to cross the Deeside 
railway near Balnacraig, and the Dee at Potarch Bridge,—shows itself here 
and again, according to information furnished me by Nicox, near the Muckle 
Ord road,—stands boldly up like a wall in the slack of Glen Dye, forms the 
summit of Mount Shade, and crosses the Birnie-slack burn, not as a single 
great band, but as several minor parallel branches. 
Throughout the whole of this extended reach, the granular felspathic base 
contains large imbedded crystals of orthoclase of dull lustre and a light fawn 
colour. So far may this great dyke be traced almost continuously ; speculation 
connects it northward and eastward at Buchanness to the Boddam black por- 
phyry, and southward with the dyke on Herscha Hill, near Auchenblae ; while 
that, in turn, may be supposed to be continued in the dyke on the south side 
of the Bervie Water, between Arbuthnot and its mouth. 
The crystal chosen for analysis was one taken from the vein near the lime- 
stone quarry at Clattering Briggs ; it was about two inches by one-half inch in 
dimensions; no pure portion sufficiently large for ascertaining the specific 
gravity could be got. 
°809 grammes gave— 
Silica, : ; 3 a fois 
From Alumina, . ; a 
Lo =. 647029 
Alumina, ; : « 19 “Lo? 
Ferric Oxide, . : : “301 
Manganese Protoxide, . ~ 223 
Magnesia, "938 
ame,. g. : Se eieeiul sino os: 
Potash, . : 2 peel geet) 
Sodas ae ; : Fao 
Water, . : : : *574 
Probable impurity, some of the less pure felspathic base ; here doubtiess 
somewhat more calcareous than normal ; possibly also quartz. : 
ee ee i ks 
