ESTHERIA MEMBRANACEA. 17 



beds of limestone, varying from 2 to 6 or 8 inches in thickness. These are composed 

 almost entirely of fragments of bones and scales of fishes (some 2 inches in length, others 

 smaller), cemented together by carbonate of lime, which, when pieces of the rock are steeped 

 in dilute acid, is dissolved out, leaving the fish-remains standing in relief. 



" A small greenstone-dyke passes through the Estheria-beds ; and not far distant the 

 rocks have been disturbed, and a great bed of bituminous shale occurs, which burns with 

 a bright white flame, and smells like fish-oil. The greenstone-dyke is not above 2 feet 

 wide ; it does not appear to have disturbed the strata. I have found other such dykes 

 since, near John O'Groat's and the Island of Stroma ; and I find that these must have 

 broken through after the flag-beds had become consolidated, because in the two latter 

 places portions of the flagstones are enclosed in a breccia-like state in the trappean 

 matter. 



" Near Wick, I have met with limestones similar to those above mentioned, enclosing 

 fish-remains, which, however, are much smaller than those in the limestone of Castle Hill. 

 Some are very minute, and, where the rock has been exposed to the weather, show thin 

 fine lines of yellow in the broken edges. All these beds take that colour wherever exposed, 

 although they are bluish or dark grey when first broken. If put into acid, they soon 

 become yellow. I believe that I have the Estheria also with these broken fish-remains at 

 Wick. Some of these thin beds of broken fish lie nearer the Estheria-beds at Castle Hill 

 than the thick beds which I mentioned. 



" All the Estheria-beds that I know are amongst the flag-beds of commerce ; conse- 

 quently, according to Sir R. Murchison's 'Siluria' (pp. 283, 432, &c), they are in the 

 middle formation of the Old Red Sandstone. 



" Sir R. Murchison mentions them as being found in Shetland. A little shell-like 

 fossil that I got on Sumburgh Head was much like one." [C. W. Peach, January 28, 

 1861.] 



Mr. John Miller, E.G.S., of Thurso, has also supplied me with information respecting 

 the local occurrence of these little fossils. He says — 



"The Estheria membranacea was discovered by Mr. Robertson, of Inverugie (Elgin), 

 in a quarry at the Peerie Sea, near Kirkwall, on the mainland of Orkney. The Orkney 

 Islands are a prolongation of the Old Red Sandstone of Caithness, possessing a well- 

 marked development of the triple arrangement characterising the Old Red series of the 

 north-east corner of Scotland, as shown by Sedgwick and Murchison more than thirty 

 years ago, and since confirmed by Sir R. Murchison in his various memoirs on the subject. 

 The Estheria occurs in the middle member of the series, or the great fish-bed. Hugh 

 Miller figured it as a molluscan shell in his well-known work, the ' Old Red Sandstone ; ' 

 and shortly after that book was published Mr. Dick found the Estheria in Caithness, at 

 various localities between Thurso and Murkle Bay, in the cliffs and shelving rocks of the 

 sea- coast. I afterwards found it in the Brownhill Quarry, a little to the south-west of 

 Thurso ; and Mr. Peach has since found it at Castle Hill. Erom this last locality to Thurso 



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