OF THE NORTH-EAST OF FIFE. 425 



We undoubtedly owe the preservation of these interesting rocks 

 to their having been let down by faults among the underlying 

 andesites, they having been thereby protected from the action 

 of denudation, which has so completely removed the younger rocks 

 from the rest of the district. 



Erom the foregoing it will be seen that in this coast-section of 

 about two miles, from Jock's Hole to Scroggieside, we have ex- 

 amples of the lavas of the three great eruptions of the Old-Red- 

 JSandstone volcanos, with specimens of the various materials ejected 

 from some of them, ranging from the great blocks of the breccia to 

 the hne ashy dust of some of the stratihed beds ; the section, there- 

 fore, is of considerable interest, but perhaps the most remarkable 

 feature of it is the ancient volcanic glass lying in the hollows of the 

 dacite lava. 



APPENDIX. 

 By Prof. John W. Judd, E.R.iS., Pres. G.S. 



Although the particular section described by Mr. Durham has not 

 been examined by me, I have had considerable opportunities of 

 making myself acquainted with the general characters and relations of 

 the igneous rocks of the district where it is exposed. In the year 1876, 

 I spent some months in examining the volcanic rocks of Angus and 

 Fife, under the guidance of the late Sir Charles Lyell, who had such 

 an intimate acquaintance with the geology of the district ; and 

 the general conclusions at which I arrived * with regard to the rela- 

 tions and ages of the different types of igneous rocks in that area 

 correspond very closely with the views which Mr. Durham has 

 enunciated in the foregoing paper. 



Among the rocks which Mr. Durham has from time to time sent 

 me for determination, there are several which, from the remarkable 

 state of their preservation and the light which they seem to throw 

 upon some very important petrological problems, appear to me to be 

 worthy of detailed description. I am greatly indebted to the author 

 of the paper, not only for the loan of his own collection of rock- 

 sections, but for the readiness with which he has supplied me with 

 ample materials for further study. Three of the ro'cks referred to in 

 this paper are particularly interesting in their characters, and may 

 be regarded as noteworthy additions to British petrography. 



The remarkably fresh rock of Northfield (see Plate XIII. fig. 1) 

 has a specific gravity of 2*68. It is a very typical pyroxene-andesite, 

 with a large amount of glassy base ; through this base, microlites 

 of triclinic felspar are scattered in great profusion, with granules 

 of pyroxene, the whole forming a felt of microlites (MicroUtJienJllz), 

 By the use of high powers, it is seen that the abundant glass be- 

 tween the microlites is filled with globulites, trichites, and belonites. 



There are no porphyritic crystals of felspar in this rock, but 



* See Quart. Journ. Geol. Soc. vol. xxxi. (1875) pp. 141-2. 



2g2 



