78 MASKELYNE. — MINERALOGICAL SPECIMENS. 



interest as being aggregates of minerals and often containing 

 crystals in cavities or otherwise distributed through them, from 

 the presence of which the history and associations of the rock 

 itself may be gathered. Hence a judiciously made collection of 

 rocks has the character of an index to the petrology of a whole 

 country. 



It is among igneous rocks that the Arctic mineralogist will 

 probably find his chief occupation. The important minerals that 

 occur under other conditions, such as where they are found lining 

 the fissures which carry mineral lodes, may indeed be accidentally 

 met with — perhaps among the weathered masses at the foot of a 

 cliff on the section of which the mineral vein may be recognised 

 from which they came ; and any minerals so found that from their 

 metallic lustre, their weight, or some other striking character may 

 appear peculiar should be preserved in specimens, so that their 

 characters may be determined at leisure. But the rocks fruitful 

 of minerals for the Expedition, north of Upernavik, will in all 

 probability be of a different kind. It is among the minerals that 

 belong to or are associated with the occurrence of igneous rocks 

 developed on a large scale that the Expedition will be able 

 probably most effectively to deal. For the conditions of Arctic 

 travel are hardly consistent with the close and careful search 

 needed for the discovery of the rarer kinds of minerals ; nor are 

 the characters of the country and climate such as to expose such 

 minerals to view under favourable conditions for finding them, as 

 for instance in the beds of torrents. However uncertain may be 

 the early accounts that recorded the existence of an active vol- 

 cano and fumerole action in the south of Greenland, it is quite 

 possible that volcanic forces may still be in action in the regions 

 of a remoter north. Should this be found to be the case there 

 will be an ample field provided for all that enterprise and obser- 

 vation can do in collecting materials for the description of such 

 a district. Some notes drawn up by an experienced observer, 

 Mr. J. W. Judd, are appended to these instructions, and they deal 

 with the more important petrological questions that arise in such 

 a neighbourhood. 



In the case of rocks of the plutonic class being met with, it 

 is less easy to offer as precise injunctions as in the former case 

 in regard to the methods of observation. A collection of well 

 selected specimens of the rocks themselves is in all cases the first 

 requisite; and next, it is important to gather illustrations of' any 

 special peculiarity in mineral associations that these rocks furnish. 

 In cases where plutonic rocks have intruded into other formations 

 it is desirable that specimens of the adjacent rock should, where 

 practicable, be collected from points at different distances from the 

 intruding mass. And in the case of rocks of the granitic class it 

 may be that irregular cavities may be met with in which the 

 crystals of the minerals forming the rock are distinctly developed ; 

 and these are sometimes associated with other minerals of interest 

 euch as beryl, topaz, tourmaline, &c. 



Among the rocks of the volcanic class the trachytes will often 

 be found rich in interest for the mineralogist, as well from the 



