Vol. 70.] OF THE COUNTRY AROUND HUNTLY. 287 



and the garnets are wholly of the pink variety. Though small, 

 these are very numerous, and are set in a matrix of felspar and 

 biotite. The felspar is now not labradorite, but andesine (/u = 1*544). 

 With the biotite occurs a titaniferous magnetite, and there seem 

 to be intergrowths of biotite and (?) felspar. Some quartz, bearing 

 rutile-needles, is present. 



The association of the minerals cordierite and hypersthene has 

 been previously recorded as occurring both in hornfelses and in 

 rocks of igneous origin. In the case of contact-altered rocks, 

 W. Ramsay l described an occurrence where orthoclase and soda- 

 orthoclase intergrown had as inclusions cordierite, hypersthene, 

 biotite, and magnetite, while cordierite and quartz filled the inter- 

 stices between the felspars. Ramsay came to the conclusion that 

 the rock was the result of contact-alteration, and noted also that 

 the cordierite gave the characteristic ' trillings ' (drilling s- 

 bildung), a rare phenomenon in a hornfels. 



Some seventeen years later a series of such rocks was described 

 from the Christiania district by Dr. V. M. Groldschmidt, who placed 

 them' in his Class IV. 2 According to this observer, 20*5 per cent, 

 of the rock is assigned to cordierite, and only 1*5 to hypersthene. 

 By a series of chemical analyses, it is proved that no transference 

 of material has taken place 3 from the igneous rock — unlike, there- 

 fore, the rock at the Rothiemay cutting. The cordierite 4 in this 

 case is untwinned, though ' trilling ' had been observed in the 

 previous Classes I and II. 5 



In Britain, as an original constituent of plutonic rocks, cordierite 

 has been hitherto found only in the Cornish granites, where it is 

 held to result from the impregnation of the magma by sediments. 6 



Two important papers, dealing with the occurrence of cordierite 

 in basic plutonic rocks, appeared several years ago. The earlier of 

 these, by Prof. A. Lacroix, deals with the intrusion of Le Pallet. 7 

 Here a gabbro-massif is situated among mica-schists, and an in- 

 sensible passage can be traced from an olivine-gabbro with labra- 

 dorite to a cordierite-norite with andesine. In the quarry of Les 

 Prinaux, xenoliths of mica-schist in gabbro occur, and are surrounded 

 by a layer of cordierite-norite that separates them from the gabbro. 

 From this, and from the field-relations, Prof. Lacroix concluded 

 that the cordierite-norite was due to the transformation of the 

 gabbro magma by assimilation of material from the mica -schist. 

 Besides the above-mentioned minerals, it is to be noted that biotite, 

 almandine, and quartz occur. 



In Minnesota, a series of similar rocks (to the gabbro type) have 



1 ' Die Alteren, die Nephelin syenite Umgebenden Gesteine' Fennia, vol. xi, 

 No. 2 (1894) pp. 45-76. 



- ' Die Kontakt-Metamorphose im Kristianiagebiete ' 1911, pp. 160-67. 



3 Ibid. p. 23. 4 Ibid. pp. 358-59. 5 Ibid. pp. 146-154. 



8 -The Geology of Dartmoor' Mem. Geol. Surv. 1912, Explan. Sheet 338, 

 p. 38 ; & ; The Geology of the Country around Newton Abbot ' Mem. Geol. 

 Surv. 1913, Explan. Sheet 339, p. 67. 



7 ' Le Gabbro du Pallet & ses Modifications ' Bull. Carte Geol. France, vol. x 

 (1898-99) pp. 341-96. 



