Graham — Pseudomorphs in McGill University Collection. 51 



gives no quantitative analysis of the material in the paper 

 referred to. It is quite possible, however, that they were 

 pseud omorphs of albite, and not orthoclase, after laumontite; 

 and Greg and Lettsom quote an analysis by Heddle of such 

 pseudomorphs from Kilpatrick, which have the composition of 

 a soda feldspar containing about one per cent of potash. 

 Hintze, however, under orthoclase, mentions pseudomorphs 

 after laumontite as occurring at Kilpatrick, and in the same 

 paragraph refers to an analysis by Bischof which he appears to 

 suggest was made on material from this locality. The same 

 analysis is given by Blum, although that author does not 

 expressly state where Bischof obtained his specimens, and on 

 referring to Bischof's original paper* I find the same uncer- 

 tainty exists even there, as it is not at all clear where the 

 material he analyzed came from. The additional fact that 

 Greg and Lettsom make no mention of pseudomorphs of ortho- 

 clase after laumontite in their Mineralogy of Scotland which 

 appeared in 1858, several years after these observations of 

 both Haidinger and Bischof, lends considerable probability to 

 the view that such pseudomorphs had not at that time been 

 found in Scotland, but that in all the observed cases the replac- 

 ing mineral had been albite ; nor are pseudomorphs of ortho- 

 clase after laumontite included in the list of British Pseudo- 

 morphs published by Prof. Miersf in 1896. However, a 

 variety of orthoclase does occur at Kilpatrick, which was 

 named erythrite by Thomson;}; in allusion to the flesh-red color; 

 this he described as a compact feldspar, which he never 

 observed in crystals, but there is nothing in his description to 

 suggest that this was of a pseud omorphous nature. 



It will be seen from the foregoing that pseudomorphs of 

 orthoclase after laumontite are of fairly wide occurrence, 

 although in the specimens from many of the localities the 

 alteration seems to be incomplete, and the crystals often more 

 or less hollow ; but in the case of the specimens from Temple- 

 ton described in this note, the crystals are invariably quite 

 solid and compact, and, except in the form, show no trace 

 whatever of a former existence as laumontite material. In 

 this complete alteration to orthoclase, and, further in the 

 small content of lithium, the mineral resembles the original 

 weissigite. 



The reverse change, from orthoclase to laumontite, has been 

 observed from at least one locality, the Hollenstein-Klamm, 

 Florenthals, Tyrol, where more or less altered adularia crystals, 

 usually coated with chlorite, are found. 



* N. Jahrb. f. Min., 43, 1850. f Min. Mag., xi, p. 263. 



X Phil. Mag., xxii, p. 188, 1843. 



