Revieics — Geological Survey of Scotland. 



323 



are of Tertiary age, a considerable number belong to the Carboni- 

 ferous period and some to that of the Old Eed Sandstone, while 

 a few are as old as the Lower Silurian period, or even earlier in 

 date than this. 



In chapter ii is given a table of formations occurring in Sheet 21, 

 and a general geological description of the area. The following is 

 a Table of the Aqueous Series observed : — 



Eecent 



and 



Post-Tertiary. 



Drift Series. 



Cretaceous. 



LlASSIC. 



Estuarine 



and 

 Marine. 



Rh^tic. 



Triassic. 



Carboniferous. 



Old Red 



Sandstone. 



Lower 

 Silurian. 



Metamorphic. 



Subaerial ( Blown sand, 



and I AUuvium of stream terraces and old lakes. 



Fresh-water. ( Peat. 



iMud and sand of present beach. 

 Raised beaches (25 feet). 

 Raised beaches (intermediate) . 

 Raised beaches (100 feet). 

 {Sands, gravels, and stratified clays. 

 Eskers and glacial shell-beds. 

 Erratic blocks. 

 Boulder-clay or TiU ; drumh'ns. 

 Ice-markings on rocks. 



Limestone with siliceous concretions, occurring in volcanic vent. 

 Dark shale with many fossils, occurring in volcanic vent. 

 Black shale with ironstone and limestone, occurring in volcanic 



vent. 

 Pale-coloured mudstones, occurring in volcanic vent. 

 Red marls and shales, with white and yellowish sandstones. 

 Thick red, yellow, and whitish sandstones, with masses of con- 

 glomerate. 

 False-bedded red sandstones. 



{Coal-measures, with contemporaneous lava. 

 Carboniferous C Upper Limestone group. 

 Limestone < Edge-coal group. 

 Series. ( Lower Limestone group. 



Calcifbrous Sandstones, with intercalated volcanic series. 

 ( Upper Red Sandstones and conglomerates, with volcanic series. 

 I Lower Red Sandstones, mudstones, and conglomerates, with 

 ( volcanic series. 



( Cherts, grits, and dark schists, associated with a volcanic series 

 \ (Arenig?), 



i Mica-schist. 

 Limestone. 

 Slate. 

 Gritty schists, or schistose grits. 



The Igneous Series are divided into : — 



A. Those which are interstratified or contemporaneous with the 



formations among which they lie : occurring in the Carboni- 

 ferous, in the Old Eed Sandstone, and in the Lower Silurian. 

 h}. Fragmental volcanic rocks subsequent in date to the strata 

 among which they lie : of Tertiary age. 



B. Intrusive or subsequent in date to the rocks among which they 



lie : of Tertiary, Carboniferous, Old Red Sandstone, Lower 



Silurian (?), and of uncertain age. 



The most effective illustrations of geological structures are given 



in the ten plates which illustrate this memoir, and deserve special 



notice. Plate ii furnishes an admirable photo-reproduction of an 



•exposure of contorted mica-schist with quartz-veins, seen in the 



