J. W. JUDD ON THE SECONDARY ROCKS OP SCOTLAND. 723 



day. In Skye and Raasay these strata, which are probably not 

 less than 400 or 500 feet in thickness, are very imperfectly exposed ; 

 but southwards, in the islands of Eigg and Muck, the series acquires 

 far greater proportions, and its characters are capable of being 

 much more accurately studied. 



The estuarine strata of Jurassic age in the Western Highlands 

 present, like those of the eastern coast of Scotland, two distinct 

 types, the arenaceous and the argillo-calcareous ; the former closely 

 resembling in characters the English Hastings Sand, the latter 

 presenting the most striking analogy in their general features with 

 our Purbeck and Punfield series. 



The Great Estuarine Series is best displayed along the north-west 

 shore of the island of Eigg, from Sgor Scalleadh to Laig Bay. The 

 divisions which can here be recognized, proceeding from above 

 downwards, are as follows i — 



feet. 



I. Strata of black shale, crowded in places with Cypris, and alter- 



nating with thin bands of argillaceous limestone. They are 

 sometimes crowded with Cyrena and Cyclas; but at others are 

 full of Palicdina, Melania, and other univalves. Beds, sometimes 

 of great thickness, completely made up of the shells of Ostrea 

 hebridica, Forbes, sometimes occur in the series, and these very 

 closely resemble the Cinder-beds of the Purbeck series. Bands of 

 fibrous carbonate of lime, like the "beef" and " bacon" bands of 

 the same formation, also occur, and fish-remains, including both 

 scales and teeth, are sometimes abundant 150 



II. A great series of sandstone beds of white and grey tints, in places 



becoming very coarse-grained and passing into grits ; occasionally, 

 indeed, pebbles of white quartz become so numerous as to convert 

 the rock into a conglomerate. These strata often exhibit much 

 false-bedding, and their surfaces are sometimes found to be 

 covered with ripple-marks, sun-cracks, and worm-tracks. In 

 certain parts of the series the rocks contain a considerable quantity 

 of carbonate of lime, and pass into calcareous grits. Thin coal- 

 seams also occur in it. With the exception of plant-remains, 

 which are at times found in a vertical position, the only fossils 

 yet detected in this division are a few casts of Cyclas, and some 

 other shells too imperfect for identification. A very striking 

 feature often presented by the beds of this division is that the 

 calcareo-siliceous rock contains great concretionary spheres, often 

 many feet or yards in diameter ; and striking mamillated and 

 botryoidal forms also occur in it*. Owing to numerous and 

 sudden changes in dip, the occurrence of frequent faults, and the 

 interruption occasioned by intrusive sheets of dolerite, it is diffi- 

 cult to estimate the exact thickness of this series, but it would 



appear to certainly exceed 500 



III. Laminated black shales and limestones like those of I., abounding 

 in Cypris and fish-remains, and shells of Cyrena, Cyclas, Paludina, 

 &c. Towards the base of the series beds of conglomerate and 

 shelly limestone occur, which abound with freshwater shells, and 

 also contain very numerous fish and reptilian remains, including 

 remains of Plesiosaurm, Ohelonians, &c 200 



* Hugh Miller first noticed and described a peculiar property which the 

 sands formed by the disintegration of these beds exhibit, namely, that of giving 

 forth a musical note when pressed by the feet in walking over them. 



