3io Probable Origin and Age. of the Sun. fj uly. 
The great Irwell fault, described by Prof. Hull,* which 
stretches from the Mersey west of Stockport to the north of 
Bolton, has a throw of upwards of 3000 feet. 
Some remarkable faults have been found by Prof. Ramsay 
in North Wales. For example, near Snowdon, and about a 
mile E.S.E. of Beddgelert, there is a fault with a downthrow 
of 5000 feet ; and in the Berwyn Hills, between Bryn-mawr 
and Post-gwyn, there is one of 5000 feet. In the Aran Range 
there is a great fault, designated the Bala fault, with a 
downthrow of 7000 feet. Again, between Aran Mowddwy 
and Careg Aderyn the displacement of the strata amounts 
to no less than from 10,000 to 11,000 feet.t Here we have 
evidence that a mass of rock, varying from 1 mile to 2 miles 
in vertical thickness, must have been denuded in many 
places from the surface of the country in North Wales. 
The fault which passes along the east side of the Pent- 
lands is estimated to have a throw of upwards of 3000 feet. I 
Along the flank of the Grampians a great fault runs from 
the North Sea at Stonehaven to the estuary of the Clyde, 
throwing the Old Red Sandstone on end sometimes for a 
distance of 2 miles from the line of dislocation. The 
amount of the displacement, Prof. Geikie|| concludes, must 
be in some places not less than 5000 feet, as indicated by the 
position of occasional outlyers of conglomerate on the 
Highland side of the fault. 
The great fault crossing Scotland from near Dunbar to 
the Ayrshire coast, and which separates the Silurians of the 
South of Scotland from the Old Red Sandstone and Carbon- 
iferous tradts of the North, has been found, by Mr. B. N. 
Peach, of the Geological Survey, § to have in some places a 
throw of fully 15,000 feet. This great dislocation is older 
than the Carboniferous period, as is shown by the entire 
absence of any Old Red Sandstone on the south side of the 
fault, and by the occurrence of the Carboniferous Limestone 
and Coal-measures lying direCtly on the Silurian rocks. 
We obtain here some idea of the enormous amount of denu- 
dation which must have taken place during a comparatively 
limited geological epoch. So vast a thickness of Old Red 
Sandstone could not, as Mr. Peach remarks, “ have ended 
originally where the fault now is, but must have swept 
southwards over the Lower Silurian uplands. Yet these 
thousands of feet of sandstones, conglomerates, lavas, and 
* Mem. Geol. Survey of Lancashire, 1862. 
f Mem. Geol. Survey of Great Britain, vol. iii. 
I Memoir to Sheet 32, Geol. Survey Map of Scotland. 
|| Nature, vol. xiii., p. 390. 
§ Explanation to Sheet 15, Geol. Survey Map of Scotland. 
