50 Graham — Pseudomorj>hs in McGill University Collection. 



These analyses were made by dissolving as much as possible 

 of a weighed quantity of the mineral in acid, and calculating 

 the results up to 100 per cent after deducting the weight of 

 the insoluble residue. Hence they do not show the actual 

 composition of the material taken, although they serve to 

 indicate that the percentage of lime falls off more and more 

 as the alteration proceeds, as also does that of the water once 

 the hardening of the material has commenced, whilst the 

 alkalis make their appearance in increasing quantities, render- 

 ing probable the assumption that the crystals are partial pseudo- 

 morphs of feldspar after laumontite. Sharp, well formed 

 crystals of adularia, exhibiting the forms {110 J, {001}, are 

 also found at Lake Superior, situated on calcite and native 

 copper, and these have also been regarded as probably due to 

 the alteration of laumontite. On the other hand, J. 1). Whit- 

 ney* has called attention to the very common occurrence of 

 orthoclase in all the mines of this region ; he describes the 

 crystals as being rarely more than a few hundredths of an inch 

 in length, of a reddish color, arranged in bunches and geodes, 

 and accompanied by native copper and the zeolites, the usual 

 vein minerals of the region. From a consideration of the 

 relative manner in which these minerals are associated with 

 one another, Whitney concluded that in .this case the ortho- 

 clase was formed contemporaneously with the accompanying 

 minerals, and that it is not a pseudomorphous product of the 

 zeolites ; from which it would appear that orthoclase does 

 occur in the veins at Lake Superior as a primary mineral, asso- 

 ciated with the zeolites, etc., although, at the same time, the 

 adularia crystals referred to above may have had a different 

 and secondary origin, as Blum has suggested. 



It is doubtful whether orthoclase has ever been found 

 replacing laumontite at any of the well known Scotch localities 

 for that mineral, notwithstanding the fact that such pseudo- 

 morphs have been described or referred to by several authors. 

 In 1848, Haidingerf examined a number of altered zeolites 

 from Allan's collection in Edinburgh, among which were some 

 flesh-red crj^stals having the angles of laumontite but the hard- 

 ness (6) and the specific gravity (2'5 to 2*8) of feldspar; the 

 crystals had drusy surfaces and were ill-defined, and in addi- 

 tion were frequently hollow or else filled with a dark green 

 stony material. These specimens were found in the trap rock, 

 associated with quartz, at the Kilpatrick Hills, near Dumbar- 

 ton, and also at Calton Hill, Edinburgh. Haidinger described 

 them as pseudomorphs of feldspar after laumontite, apparently 

 relying on qualitative tests in their determination, since he 

 * This Journal, xxviii, 16, 1859. f Sitz. Akad. Wien, iii, 95, 1848. 



