286 BATHYMETRICAL SURVEY OF 



parallel to those in the Moine schists ; indeed, in certain localities they 

 pass, irrespective of the boundary-line, from the igneous to the altered 

 sedimentary rocks. 



On either side of the Sutors of Cromarty, and stretching southwards 

 along the sea-cliff to Fortrose, there is a narrow belt of crystalline schists 

 rising from underneath the Old Red Sandstone. They belong to the 

 group of quartz biotite granulites, and are associated with bands of 

 amphibolite. 



Newer granite masses are also represented in the area, as, for 

 instance, on the hills north of Ardross Castle above Strath Rusdale, 

 and in Glen Orrin west of Fairburn House. They resemble the normal 

 types of the newer granite masses of the Highlands, and were erupted 

 after the Moine schists had assumed their present crystalline character. 



The strata of Old Red Sandstone age in the basin of the Cromarty 

 firth are arranged in the form of a great syncline, whose axis runs in a 

 north-north-east and south-south-west direction. The base of the series 

 and the order of succession are admirably displayed on the sea-cliffs at 

 Cromarty, and on the south-east shore of that firth as described long 

 ago by Hugh Miller. The basal conglomerate is there overlain by the 

 well-known fish-band, with calcareous nodules, graduating upwards 

 into the coarse sandstones that form the centre of the basin. On the 

 west side of the firth a similar sequence is observable. The basal con- 

 glomerate along the flanks of the hills is usually brought into conjunction 

 with the crystalline schists by a fault, evidently of no great amount, for 

 the unconformity is visible at certain localities. This horizon is sur- 

 mounted by red sandstones and flagstones, calcareous and bituminous 

 shales, and occasional intercalations of clays with limestone nodules, 

 with fish remains. These are followed by an upper band of conglomerate, 

 which is overlain by the coarse sandstones in the centre of the basin. 



Various outliers of Old Red Sandstone, largely composed of con- 

 glomerate, and resting unconformably on the highly denuded platform 

 of crystalline schists, occur some miles to the west of the main area of 

 this formation in the Conon basin. Some of these are met with on the 

 plateau between Loch Luichart and Aultguish. By far the largest and 

 most important is that still further north in Strath Vaich, where an 

 extremely coarse conglomerate, composed largely of blocks of the 

 contiguous foliated granite, is found on the crest of Meall a' Ghrianain 

 (2531 feet). 



At the base of the sea-cliff formed by the crystalline schists and Old 

 Red Sandstone of the Black Isle and the North Sutor, there are small 

 patches of Oolitic rocks which have only a limited development. They 

 occur on the beach below high-water mark at Eathie and at Port-an- 

 Righ and Cadh-an-Righ near Sandwick. By means of the great fault 

 that traverses the line of the Caledonian Canal, and is continued 

 north-east along the shore of the Black Isle, these Secondary strata 

 have been let down against the older rocks. 



