680 J. W. JUDD ON THE SECONDARY ROCKS OF SCOTLAND. 



IV. General Characters and Succession op the Secondary Strata 

 oe the Western Highlands. 



In describing the Mesozoic rocks of the Eastern Highlands, we 

 had occasion to refer again and again to the freqency with which 

 deposits of marine origin alternate with others that exhibit clear 

 evidence of having been accumulated under estuarine conditions. As 

 we have already shown, this alternation of marine and estuarine 

 strata constitutes the most salient and striking feature throughout 

 the whole series of Secondary formations in Sutherland and on the 

 east coast ; and in the equivalent deposits on the western coasts and 

 islands, the same phenomenon, if exhibited in a less marked degree, 

 is nevertheless sufficiently common to impart to these strata charac- 

 ters by which they are strikingly distinguished from most of their 

 English representatives. 



Thus we find in the Mesozoic series of the Western Highlands 

 that there occur in the Infralias beds in some localities a mass of 

 sandstones with thin coal-seams ; while the whole of the formations 

 included between the Parkinsoni-heds of the Inferior Oolite and the 

 middle portion of the Oxfordian are represented over a considerable 

 area by a series of estuarine deposits, which probably attain in places 

 to a thickness little short of 1000 feet. Even where distinct evi- 

 dences of estuarine conditions are wanting in the Hebridean Jurassic 

 strata, the deposits are clearly, as a general rule, of more littoral 

 character than their equivalents in England — beds of conglomerates 

 and other indications of the proximity of a shore-line making their 

 appearance at a great many different horizons in the series. 



We have pointed out the existence among the Jurassic deposits of 

 the eastern coast of Scotland of two distinct types of strata of 

 estuarine origin — one argillaceous or calcareo-argillaceous in compo- 

 sition, and resembling the Purbeck and Punfield series in the south ; 

 and the other mainly arenaceous in composition, and resembling por- 

 tions of the English Hastings sand and Carboniferous formations. 

 So strikingly, indeed, do the former class of strata — with their bands 

 of limestone made up of Cyclas, Cyrena, or Paludina, their lami- 

 nated shales crowded with Cyprids, their thick masses of dwarfed 

 oysters (" cinder-beds "), and their seams of fibrous carbonate of 

 lime (" beef- and bacon-beds ") — resemble the series of deposits 

 found at the base and summit respectively of the great English 

 Wealden formation, that it is by no means surprising that, before 

 their relations to the marine beds were made out, Murchison should 

 have supposed that he had detected veritable Wealden deposits in 

 the Western Isles. 



But in the case of the llesozoic series in the West of Scotland we 

 find evidences of a still more interesting character, namely, that the 

 tendency to a recurrence of estuarine conditions during the whole of 

 the Jurassic period was continued all through the Upper Creta- 

 ceous. Although, as I have pointed out in my former paper, there 

 is strong evidence that considerable patches of Cretaceous strata had 



