138 J. W. JUDD ON THE STRTJCTUKE AND 



portion of the agglomerates should be referred. Of this we have a 

 striking illustration in the fact that certain rocks, classed as unstra- 

 tified agglomerates in the Survey Memoir published in 1861, are 

 referred to the stratified tuffs in the 6 -inch map of 1864. 



III. The unconformity between the rocks of the upper and lower 

 parts of the hill respectively would seem at first sight to be very 

 clearly proved by the section which is represented in the Survey 

 Memoir (page 23, fig. 5). 



1. It must, however, be noticed, in the first place, that the rocks 

 exhibited in this drawing are not presented in a vertical section, 

 but in a slope of about 45° ; and, consequently, the appearances do 

 not warrant those conclusions of overlap and unconformability which 

 have been drawn from them. 



2. The supposed evidence afforded by this section, as given in 

 1861, was virtually abandoned in 1864, when, in the 6-inch map, 

 a portion of the supposed overlapping agglomerates are placed 

 (doubtless correctly, as an examination of the spot will prove) 

 with the contemporaneous and interstatified tuffs of the base of 

 the hill. 



In order to make this matter clearer, I subjoin a. copy of the 

 original drawing, and one of it as now amended in conformity with 

 the 6-inch map of the Geological Survey, representing the relations 

 of the rocks seen beside the Queen's Drive (see figs. 1 & 2). 



IY. A mass of lava proceeding from the great basaltic cap of 

 the Lion's Haunch has been supposed by Professor Geikie to repre- 

 sent a " neck " from which lavas flowed during the second period 

 of eruption*. 



That this is the true explanation of the appearance referred to 

 I feel the gravest doubt ; but if it be so, it seems to be decisive 

 as to the subsequent uptilting of all the rocks composing the hill. 

 A reference to the 6-inch map will show that the elevation of the 

 supposed orifice of the " neck " is about 500 feet above the sea, 

 while the upper edge of the mass, which it is suggested flowed from 

 this orifice, is about 700 feet. Consequently it is clearly impossible 

 that the mass of lava capping the Lion's Haunch could have flowed 

 from this vent and spread around it in its present position, in the 

 manner it is represented to have done by Professor Geikie. But it 

 has long appeared to me that a .more probable explanation of the 

 appearances seen above the Queen's Drive is the following : — that 

 a great current of basaltic lava issuing from some point above has 

 filled up a fissure opened in the mass of agglomerates over which it 

 flowed. Dykes thus filled from above have been detected not unfre- 

 quently in volcanic districts. 



Maclaren, indeed, regarded the mass of lava capping the Lion's 

 Haunch as a portion of the same current that is seen below the 

 churchyard of Duddingston, which it unquestionably very closely 

 resembles in its somewhat peculiar mineral characters. If this 



* Memoir on the Geology of the neighbourhood of Edinburgh (1861), 

 p. 124. " The Geology of Edinburgh and its neighbourhood." An address to 

 the Geological Section of the British Association (1871). Keprinted, p. 25. 



