PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND, 267 
any other locality,—is cream-coloured, and possibly somewhat altered by 
incipient weathering ; it does not show striation. From the centre of one of 
these crystals, however, a clear colourless translucent portion was obtained, 
which was distinctly striated: here then, one and the same crystal had a striated 
and an unstriated portion, the striated being inside. 
We are hardly therefore justified in going even the length which Corra 
does when he says—‘“‘ This striping, when observable, is a very characteristic 
sign ; but its absence is not equally so.” 
But it can only profess to be characteristic as between the ortho- and the 
plagio ; for its being seen indiscriminately, sometimes in coarse pattern, some- 
times of microscopic minuteness, among all the plagioclastics, renders it inap- 
plicable as a mode of discriminating among ¢hem; and there is reason to believe 
that the time even now is, when it is more imperative that the field geologist 
should be able to determine between the various plagioclastic felspars, than 
even to recognise “ common felspar.” 
As regards striation, then, its presence enables us to say very litile,—its 
absence confers upon us no absolute knowledge whatever. 
Let us now see what aid we derive from specific gravities. 
The specific gravities of Scottish Orthoclases, numerically arranged, are 
the following,—the numbers being in some cases the mean of several deter- 
-minations :— 
Pitfechie Monnymusk, Aberdeen, 2°503 | Lairg, Sutherland, 2:555 
Glen Fernate, Perthshire, 2° 525 Scaire Ruidh, Harris, 2° 555 
Ben-na-chie, Aberdeen, 2-534 | Anguston, Aberdeen, 2° 555 
Ben Resipol, Argyle, 2°538 | Scoltie Hill, Aberdeen, 2° 555 
Blackwater, Ross-shire, 2°54 Midstrath, Aberdeen, . 2250) 
Loch of Leys, Aberdeen, 2°542 | Glen Beg, Glenelg, 2° 558 
Struay, Ross, 2°544 | Rubislaw, pinkish, 2-559 
Sclattey, Aberdeen, 2°545 | Shinness, Sutherland, . 2°56 
Canisp, Sutherland, 2°545 | Cowhythe, Banffshire, . 2°56 
Froster Hill, Aberdeen, 2°548 | Spyhill, Kincardine, 2° 562 
Yestnaby, Orkney, 2°549 | Rubislaw, grey, ; 3 2-502 
Rinashat, Aberdeen, 2°55 Geo-na-Shermaig, Cape Wrath, 2° 563 
Blirydrine, Kincardine, 2°551 | Ben Capval, Harris, 2° 565 
West Stocklet, Harris, . : 2:552 | Tongue, Sutherland, 2° 569 
Rubislaw, Aberdeen, . : 2°554 | Stromay, Harris, . 2° 574 
Lua yayi, Erribol, Sutherland, 2-554 | Pitfodles, Aberdeen, 2:579 
Torry, Kincardine, 2-554 | Cowhythe Head, Banff, 2:58 

The average of these thirty-four is 2°553: the number 2° 555 (occurring five 
times) may be more easily retained in the memory. The range «077 is so small 

