296 Mr. MuRCHisoN on the Coal-field of Brora in Sutherland shire, 



sents on its northern bank^ for nearly a mile and a half above its mouth, a 

 broken succession of low cliffs, consisting of yellow micaceous sandstone, and 

 dark coloured micaceous shale with belemnites, &c. At the first emergence 

 of these cliffs, the river quits them and bends to the south, incircling in its 

 course a trough of low land called the Pool, bounded on the south by table- 

 shaped hillocks covered with diluvium. It then enters a narrow gorge, 

 where the sandstone and shales are exposed on each bank to the height of 30 

 or 40 feet, and are visible from thence without interruption during the re- 

 mainder of its course, which continues for about half a mile. 



The highest eminences in the vicinity are the rounded hills of Braambury, 

 situated a mile and a quarter from the sea. A portion of their surface, un- 

 like that of every other elevation near them, is bare of diluvium; and the 

 exposure of the valuable freestone of which they are composed, has led to the 

 extensive quarries now worked there by the direction of the Marquess of Staf- 

 ford*. Though probably not less than 200 feet above the level of the sea, 

 with a dip conformable to that of the inferior strata containing coal, this stone 

 is noi to be traced beyond the hills where it is quarried, and may therefore 

 be considered as an isolated portion of a stratum, the continuation of which 

 has been removed, probably by denudation. 



The exterior surface of this rock is channelled into undulating grooves, and 

 the dip of the beds is easterly, at an angle of 25° to 30°. Where quarried 

 for use they consist of a remarkably white quartzose sandstone, without ad- 

 mixture of iron or any discolouring matter. In other beds the cement and 

 grains are united into one homogeneous quartzose mass, the thinner layers 

 of which are of so compact a structure as to have been used for gun-flints : 

 the extreme whiteness of some of these beds is strongly contrasted with small 

 black portions of lignite imbedded in them. Numerous casts of fossils abound, 

 with large stems of plants ; some of the former, particularly three new spe- 

 cies of pecten, are remarkable for the shaipness and minuteness with which 

 they have retained the impressions of the shells, it being diflicult to imagine 

 how the siUceous grains of which this rock is composed, could be united into 

 so uniform a paste. All the fossils now presented to the Society for the illus- 

 tration of this memoir have been examined by JNIr. J. Sowerby; and with his 

 kind assistance 1 have annexed a tabular view, referring them to their ana- 

 logues in England. 



The freestone of Braambury and Hare Hills is in some places overlaid by 



* This white freestone is in actual use for the construction of the interior of London Bridge, 

 for which purpose it seems admirably adapted by the compactness of its structure and the vast 

 size of its blocks. 



