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OLD RED SANDSTONE OF WESTERN EUROPE. 445 
many quarries to the south and north of Dingwall. They seem to spread over 
most of the basin or valley in which the Cromarty Firth lies. Down that 
hollow, as S—EDGwick and Murcutson pointed out, a synclinal fold of the Old 
Red Sandstone runs, the strata being sharply bent up on the east side against 
the ridge of metamorphic rocks on which stand the Sutors of Cromarty. On 
that side of the trough the fish-bearing clays and nodules rise to the surface 
from under their overlying sandstones and conglomerates. They were first 
made known by Hucu Mitzer as occurring at Cromarty on both sides of the 
ridge of the oider rocks. His original section* shows that the fish-bed, which 
he has made world-famous in the history of geology, lies upon a band of con- 
glomerate which rests directly upon the gneiss of the Sutor, and that it is 
overlaid by yellow sandstone. It is a band of the usual grey clay, full of 
caleareous nodules like those on the south side of the Moray Firth. The 
most characteristic organisms in these nodules are—Croccosteus cuspidatus, C. 
decipiens, Diplacanthus longispinus, D. striatus, Glyptolepis elegans, G. leptopterus, 
Pterichthys Milleri, P. oblongus. 
The axis of the Black Isle is prolonged across the mouth of the Cromarty 
Firth into the northern Sutor. On the east side of that ridge the Lower Old 
Red Sandstone again appears in conglomeratic masses, which dip away from 
the nucleus of crystalline rocks. North of Shandwick these lower strata, which 
appear to be equivalents in time and position of the lower conglomerates of the 
Moray Firth, pass upward into red flaggy sandstones, grey flagstones, blue 
shales, and thin limestones, which, like the strata of Culloden Muir, have many 
of the peculiar lithological characters of the true Caithness flags. Among these 
strata SEpGwick and Murcuison found fragments of fossil fishes.t More 
recently the Rev. Dr Gorpon and Dr Joass have re-examined the locality and 
have obtainec from it Coccosteus and other undoubted Caithness ichthyolites.t 
Professor Harkness has described the coast section.§ He estimates the lower 
sandstones and conglomerates to be 1500 feet thick, succeeded by 350 feet of 
the flaggy and shaly beds in which fish remains occur. My estimate would 
considerably increase the depth of the latter series. It is evident, however, 
that even on the largest allowance we have here but a feeble representation of 
the vast masses of the Caithness Old Red Sandstone. Nevertheless, we see 
the same agreement alike in lithological characters and in fossil contents which 
is presented also by the rocks on the south side of the Moray Firth. 
A little beyond Geanies the flaggy and shaly ichthyolitic strata, which have 
a prevalent dip towards N.N.W., are abruptly succeeded by a series of yellow 
* “Old Red Sandstone.” Plate of Sections, figs. 4 and 5. 
+ Op. cit. p. 150. 
t “Quart. Journ. Geol. Soe.” xix. p. 507. 
§ Op. cit. xx. 437, 
VOL. XXVIII. PART It, DZ 
