Mr HOPKINS. ON RESEARCHES IN PHYSICAL GEOLOGY. 



7.5 



to allude to some cases of injection described by M'Culloch \n tl 

 A^estern Islands, in which the injected beds assLe fo' eoti e .1: 

 distances the appearance of being regularly interstratified, thus em n 



n.ght be thought, to ofFer exceptions to the rule I have deZS' 

 from theoretical considerations. Four or five onlv of f. ^^'^ ^cd 



I tlun. l.ve been expressly .mentioned VirlLll'^^L^rZ 

 coast of Trottern:sh in the Isle of Sky, which appear to be the mos 

 striking, are described as follows: 



" In one case, which occurs not far from Holme there i. . h. i 

 extendmg for a great way, surmounted by a parallel sL of e 

 secondary strata m contact with it; but on a narrow inspection 

 numerable veins are seen branching into the strata in evei-y pli^L" 

 direction, mustrating in a very perfect manner the origin of at a 

 one order of veins. In a second case, three beds of trap%an be tr ced 

 .n a para lei direction for a considerable space, separated' by the regular 

 strata, when suddenly the whole unite into one mass. Had nof tW 

 occurrence at length betrayed the true nature of these beds, there tc^dd 

 have been no hesitation, from a limited observation, in deLribing th n' 

 as unquestionable instances of alternation. In the last case which I siu 

 ■nention, one regular bed of trap may be traced for more than a m e 



locks. On a sudden, however, it bends downwards so as to pass throui 

 the strata immediately in contact, and then continues to hold ts regiTar 



:zJrjx:*y''^ ''''' -''' - '''-'-- -^ p-«^'' «: 



The first of these instances presents in its branching veins exactlv 

 the phenomena which, I have been contending, must necessaril'y attend 

 any extensive horizontal injection of a fluid mass. The others seem to 

 uidicate the possibility of this injection without such phenomena, for 



bli r b bT"J n ' """ "^^ ^" ' •^^P^^^'^ *° ^-bt this possi- 

 bility, though I should in general consider a horizontal injection of that 

 extent without ramifying veins, as extremely improbable, and especially 

 if the injected bed were not a very thin one. In fact, however, there 

 • Description of the Western Islands of Scotland, Vol. i. p. 382. 



