1873.] JUDD THE SECONDARY ROCKS OF SCOTLAND. 149 



It is possible that, during the " infra-Liassic " period, beds of 

 conglomerate like those of the Dunrobin reefs may have been 

 formed at one point while strata like those of Linksfield were de- 

 posited at no great distance. In fact we have a perfectly similar 

 example in the south-west of England in the " Lias- conglomerate " 

 of South Wales and the Bhaetic Shales of the Bristol Channel. On 

 the other hand it is very probable that associated with the beds of 

 Lower-Lias age which contain coal-beds and are so imperfectly ex- 

 posed at Dunrobin, the exact counterpart of the Linksfield shales 

 may exist. At the same time, the presence of beds iii this district 

 formed under similar estuarine conditions at various horizons during 

 the Jurassic period will justify us in hesitating to fix absolutely the 

 age of the isolated strata of Linksfield, in the absence of more precise 

 palaeontological evidence. 



A number of fragmentary masses of strata similar to that of Links- 

 field have been found at several places in the neighbourhood — namely, 

 at Maryhill, Pitgaveny, Spynie Hill, and "Waukmill. 



The close resemblance between the fossils of the strata at Links- 

 field and those so admirably described by M. Hebert in very similar 

 beds at Hogonas, in Sweden, if it does not warrant the absolute 

 identification of the two series, affords strong grounds for the sus- 

 picion that they are on nearly the game geological horizon. 



§ 3. The Loiver Lias. 



The conglomerates and sandstones on the shore at Dunrobin, which 

 we have shown reasons for regarding as of Bhaetic age, are covered 

 conformably by, and, indeed, appear to graduate into, an interesting 

 series of estuarine strata, composed of sandstones, shales, and beds 

 of coal, and attaining a very considerable thickness, which I esti- 

 mate from the angle of dip and breadth of outcrop to be not less than 

 from 400 to 500 feet (see fig. 14, d, page 143). Unfortunately these 

 strata are very imperfectly exposed ; for under ordinary circumstances 

 only the harder beds appear as reefs upon the shore ; when, however, 

 the beach is temporarily scoured away by heavy storms, the bassets 

 of the softer strata of clay and coal are sometimes exposed. It was 

 thus that a bed of coal was exposed to the E.N.E. of Dunrobin Pier, 

 which led in the year 1770 to a boring being undertaken in the Summer- 

 house Park adjoining. The only record of this boring which remains 

 states that "two thin seams of coal were proved, but not deemed worth 

 working." 



The sandstones of this series appear to present the usual charac- 

 teristics of the arenaceous type of the Jurassic estuarine beds. They 

 sometimes contain numerous laminae of carbonaceous matter, and at 

 others are crowded with vertical plant-markings, like the so-called 

 "root-beds" of the Midland district of England. In one of the 

 highest of these beds of sandstone I detected casts of Pecten and 

 other marine shells, indicating that there is a gradual passage from 

 these estuarine strata to the marine beds overlying them. The 

 carbonaceous seams associated with the series appear to be well- 



