422. PROFESSOR GEIKIE ON THE 
DD. Basin, of.the Northern, firth, 
Within the area included under this name, I place all the Old Red Sand- 
stone lying on the mainland of Scotland to the north of the Grampian chain, 
except Caithness and the north of Sutherlandshire. It appears to have formed 
originally one great basin of deposit, or at least a connected series of minor 
basins. It presents strongly marked lithological distinctions from the Caith- 
ness and Orkney region, which may have been either a portion of the same basin, 
but so far from shore as to possess a very different kind of bottom, and to 
receive a strikingly distinct set of deposits, or an adjoiming but more or less 
completely isolated area. 
It will be seen from the map, that while from the coast of Banffshire at 
Buckie a continuous belt of Old Red Sandstone extends along the southern 
margin of the Moray Firth westwards to Inverness, this does not by any means 
represent the original limit of that system here, or include all the remaining ~ 
tracts in which portions of the system still survive. Small outliers occur on the 
coast to the east of Buckie, while larger areas extend inland, and even pene- 
trate far upward into the heart of the Highland mountains. That the descrip- 
tion of the main mass may not be interrupted, but may be followed in order 
round the whole of the basin, it will be convenient to take the outliers first. 
1. The Outliers.—Passing, then, across the great ridge of the Scottish High- 
lands, we first encounter at the mouths of the Don and Dee deposits which are 
no doubt referable to the Old Red Sandstone. They consist of a soft red and 
grey coarse conglomerate and red sandstone. The conglomerate, formed chiefly 
of rounded blocks of grey granite, with angular and sub-angular pieces of gneiss, — 
schist, quartz, and other metamorphic rocks, imbedded in a loose ferruginous- 
granite sand, is seen on the Don below the old bridge of Balgownie, dipping 
gently to E.S.E., and resting on the upturned edges of the gneissose rocks. 
Similar deposits have been met with in sinking wells and in other subterranean 
operations at Aberdeen.* As the outlier is bounded both towards the sea and 
inland by the crystalline masses, it seems to lie in a narrow strip, the mere end, 
perhaps, of a larger mass now concealed under the sea. It will be seen how 
A. GiBson, at my suggestion, undertook a further examination of the Old Red Sandstone of these 
islands, and prepared an essay on the subject, which he submitted to the Senate of the University of 
Edinburgh as his thesis previous to presenting himself for examination for the degree of Doctor in 
Science. Since the foregoing pages were written, the essay has been published, and I am glad of this 
opportunity of referring to it. He has traced the faults with care, and has extended his observations 
to Foula, where he finds red and grey sandstones similar to those of Shetland rising into the vast 
sea-precipice for which this island has long been famous. See his “ Old Red Sandstone of Shetland.” 
Edinburgh, 1877. [See note appended to the present Memoir. | 
* See Hucu Minizr’s “ Old Red Sandstone,” 4th edit. p. 54, note. 

