320 The Rev. Mr. Farquharson's Additional Remarks 



gray dast with which it is invested, but without dissolving it. 

 The microscope shows the remainder to consist of two parts, the 

 greater of which is composed of small grains of angular quartz, 

 scratching glass, — ^the less of similar grains of a dark red substance, 

 retaining its colour when heated, and of less specific gravity than 

 the quartz. These red particles are not attracted by the magnet, 

 but are slowly acted upon by muriatic acid, aided by heat. The 

 substance, therefore, consists chiefly of a quartz sand, mixed with 

 grains of one or more compound minerals ; and if it has proceed- 

 ed from a volcano, has probably been the dust of the various volca- 

 nic products, collected first on the sides and in the hollows of the 

 crater, and afterwards dislodged and committed to the winds by 

 some eruption more violent than usual." 



ART. II. Remarks on Mr. George Don's opinion on the varieties 

 of the Scotch Fir, (Pinus Sylvestris.) By the Rev. J. Far- 

 QUHABsoN, F.R.S. (Extracted from a Letter to the Editors.) 



I EMBRACE this Opportunity of making known the results of very 

 numerous observations which I have recently made on the exten- 

 sive fir plantations in this neighbourhood, in reference to Mr. Geo. 

 Don's opinions, first made known to me by your note to my paper 

 " On the Native Forests of Aberdeenshire," Vol. II. p. 6. Every 

 opinion on botanical questions bearing the sanction of that distin- 

 guished name, must be treated with high resj)ect ; and it is with 

 great deference that I suggest conclusions at variance Avith his. I 

 find that the horizontal branches, and relatively broad and glau- 

 cous leaves, and smooth bark, are very extensively characteristics 

 of such trees, in our fir plantations, as have accidentally abundant 

 room for a free growth. Ought they not, therefore, to be account- 

 ed rather s)'-mptoms of healthy vegetation, than marks of difl^erent 

 species, or even varieties ? I can discover no leaves without minute 

 serratures ; and although in the broader leaves the serratures 

 are frequently a little turned in from the margin towards the 

 flat side of the leaf, yet the rule is not uniform. In regard to the 

 cones, I find several instances' where they vary as much in form on 

 the same tree as they do through the whole plantations ; and on 

 the same tree also I find them often varying very considerably in 

 smoothness. 



The paucity of the cones, on healthy and vigorous trees, is in 

 accordance with one part of the economy of other species, which 

 seldom produce much fruit while they are going strongly to wood. 



But even granting that there are permanent varieties, or distinct 

 species of the Scotch fir, and the full validity of those distinctions 

 which Mr. Don has indicated, I am yet enabled to state one cir- 

 cumstance, which leaves the argument against thick planting in its 



