[ 599 ] 



XLT. — On some remarkable Dikes of Calcareous Grit, at Ethie in 



Ross-shire. 



By II. E. STRICKLAND, Esq., F.G.S. 



[Read March 7th, 1838.] 



I AM desirous of calling the attention of the Society to some remarkable 

 dikes which penetrate lias schist at Ethie, near Cromarty. The beds of lias 

 at this place have been described by Mr. Murchison in our Transactions*, 

 and their relations are given in the accompanying wood-cut (p. 600). These 

 beds are only exposed at low water, and dip towards the sea at an angle which 

 gradually increases in approaching high-water mark, where they become 

 perpendicular. Cliffs of gneiss and red conglomerate rise immediately from 

 the shore, but the broken fragments which are scattered near high-water mark, 

 conceal the actual junction of the lias with these older rocks. 



The dikes, which are here seen to penetrate the lias, are remarkable for 

 their mineral character, which so precisely resembles that of certain altered 

 quartzose sandstones, that it is impossible to refer them to a purely igneous 

 origin. 



The substance of which they are composed, is intensely hard. On exa- 

 mining it with a lens, its component particles are distinctly seen, and bear 

 the closest resemblance to ordinary water-worn grains of sand. The stone is 

 penetrated by carbonate of lime, which produces a slight etfervesence on the 

 application of an acid; and it has assumed a pseudo-crystalline structure, 

 which exhibits, when held in certain lights, the peculiar lustre of the calca- 

 reous sandstones of Fontainebleau and other places. 



A careful examination of the locality sufficed to show, that however much 

 this rock might resemble an aqueous product, yet that it forms genuine intru- 

 sive dikes, penetrating the lias shale in all directions. A and B are two dikes 

 (see the wood-cut) which are parallel to the stratification of the lias shale, 

 and their injected origin is not consequently immediately apparent ; butC is a 

 dike which sends off branches in various directions, and in no part of its 



* Second Series, vol. ii. p. 308. 



