600 H. E. Strickland, Esq., on some Dikes at Ethie, Ross-shire. 



course is parallel to the strata which it penetrates. The thickness of this dike 

 is about one foot, and that of its lateral offsets from three to six inches. D is 

 the largest dike of all, being three feet thick, and ranging parallel to the shore 

 for at least 200 yards. In one place, it also gives off a lateral branch, which 

 extends a few yards and then rejoins the main dike. 



These several dikes exhibit no variation whatever in their texture or com- 

 position, except being occasionally penetrated by small veins of carbonate of 

 lime. They show no signs of lamination, but are frequently fractured trans- 

 versely to their own direction. The transition is instantaneous from the dike 

 to the lias shale, which seems to have suffered neither alteration nor contor- 

 tion by the intrusion of this extraneous matter. The shale, from its greater 

 softness, has been washed out between the dikes, leaving them to project like 

 walls from one to three feet in height*. 



I have been the more exact in describing this locality, because the identity 

 of the specimens here exhibited with ordinary stratified sandstone is so perfect, 

 that the clearest evidence was necessary to prove that they had been inserted 

 into fissures of the lias subsequently to its deposition. The sedimentary struc- 

 ture of this rock forbids us to refer it to igneous injection from below, and 

 notwithstanding the complete resemblance of these intrusive masses to ordi- 

 nary plutonic dikes, we have no resource left but to refer them to aqueous 

 deposition, filling up fissures which had been previously formed in the Lias. 

 We have no clue to the period at which this insertion of sand into fissures of 

 the lias took place, no fossils having been noticed in the substance of the dikes 

 themselves. 



In speculating on the causes of this phenomenon, we should bear in mind 

 the total absence of trappean rocks on the eastern coasts of Ross-shire and 

 Sutherland, and the presence of vast masses of granitic and syenitic rocks, 

 which have been shown by Mr. Murchison to have been erupted subsequently 

 to the deposition of the oolitic series. 



* Mr. Murchison, in his paper on Brora, (Geol. Trans. 2nd Series, vol. ii. p. 304,) mentions a 

 dike of quartz rock as occurring at Kintradwell, on the coast of Sutherland. That gentleman has 

 further informed me, that in company with Professor Sedgwick he noticed similar dikes, both at 

 Ethie and at other places on that coast. 



