
208 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
result of a rapid and nearly simultaneous crystallisation ; the mineralogist and 
chemist with one or other of a series of superimposed epallelogenetic crystal- 
lisations ; the sequential products of a long-protracted deposition and growth 
of matter. In the change of state assumed by the fluent or plastic rock, its. 
atoms have rushed towards solidity. Inthe formation of what the Abbé Havy 
called “the gems of crystallisation,” the atoms, under the guidance of the 
crystallipolar force, have, with slow and stately march, assumed their destined — 
positions, jostling aside only the foreign substances which all great crystals 
loathe. . 
The geologist of the present day, moreover, from the limited range of his © 
familiarity with minerals, is incapable of estimating the quality of the chemist’s 
work ; and it so happens that it is just the few minerals with which the former — 
interests himself which are most commonly and most largely contaminated with 
foreign and included matter. Felspar, with its spangles; micas, with their 
crystals ; quartz, with its fluid cavities ; garnets, with its granules; and pitch- 
stones, with what the geologists call “hairs,” which, being crystals of actynolite, 
are just as far removed from hairs, as an inorganic substance is from an organic. — 
But while it is easy to repel these criticisms, it must be admitted that this 
part of the chemist’s work calls for an amount of patience and mineralogical 
discrimination not always, it is to be feared, exercised. The writer, who 
. invariably reserves the final examination of a picked mineral as his own work, — 
was never yet able to educate an ‘assistant’s eye so as to thoroughly accom-_ 
plish the separation of quartz from oligoclase ; but he trusts the perusal of 
‘the subjoined letter from a former assistant will satisfy all geologists that 
- conscientious care had been carried to the very limits of human patience :— 
3 EDINBURGH, June 31, 1876. _ : 
Drar Dr HEDDLE,—In reply to your note asking me to say how long I was engaged at F 
the picking out of the Withamite, I have to say that-it was my regular employment, when not — 
called away for a temporary matter, from March to July, both inclusive, of Session 1873-74, 
and for some weeks of Session 1874-75.—I am, yours truly, 
; R. M. .Murray. 
In order, however, to meet as far as possible all criticism on this score, the — 
associated minerals—the contact minerals—and the conjectured possible im- 
purity, will, under each: analyses, be stated. It has also to be mentioned that, 
wherever practicable, portions of the ‘material selected were, in thin’ slices, 
examined under the microscope by ordinary and by polarised light. 
