J. G. Goodchild — Deutozoic Rocks of North Britain. 599 



-or even older strata, including the metamorphic rocks of the Southern 

 Highlands of Scotland. What has been taken as the Caledonian Old 

 Eed in the cases where it has been supposed that a passage exists is 

 in reality a series of quite different age. These rocks to which 

 reference has just been made, being typically exposed in Lanarkshire, 

 I have named the Lanarkian Rocks. These are the strata which, 

 with part of the Upper Ludlow rocks, have lately been termed the 

 Downtonian Series — a particularly ill-chosen name, as it seems to 

 me, because the name Downtonian had previously been used to 

 denote all the Silurian strata above the top of the Lower Ludlow 

 Rocks. These Lanarkian Rocks form the upward continuation 

 of the true Ludlow Rocks, and they clearly mark the oncoming 

 of the continental conditions which brought the Silurian Period 

 to a close, and marked the advent of those geographical conditions 

 which ushered in the Devonian Period in what is now the 

 northern part of the Kingdom. Their stratigraphical details need 

 not be given here, for the reader will find them fully described 

 in the Geological Survey Memoir on the Silurian Rocks of the 

 Southern Uplands of Scotland — which, by the way, is one of the 

 finest memoirs issued by the Department to which I have the honour 

 to belong. 



A study of the excellent sections given in the work just referred 

 to will suffice to show that the Lanarkian Rocks have shared in all 

 the disturbances to which the Silurian Rocks have been subjected. 

 These disturbances had ceased, and had been followed by prolonged 

 denudation, long before the oldest member of the Caledonian Old Red 

 was laid down. Hence it results that the great unconformity, so 

 often referred to, passes above what is left of the Lanarkian Rocks. 

 There is no clear evidence of any unconformity below them. 



If we talfe the original red colour of the sandstones in these 

 Lanarkian rocks as evidence of their representing the very lowest 

 ^ Old Red ' (which it seems reasonable to do), then it would be these 

 rocks which form the true ' Lower Old Red,' and as such they were 

 most admirably described many years ago (1860) by Sir Archibald 

 -Geikie. There are, however, no rocks containing Silurian fossils 

 above them, nor do they present anywhere more than an accidental 

 appearance of a conformable passage into the Caledonian Old Red ; 

 indeed, in the only section where these two have the same dip their 

 interrelationship is similar to that of the Trias on the Upper Old 

 Red near Elgin. 



I have formerly ventured to speculate (on what seem to me to be 

 good grounds) whether these Lanarkian Rocks might not have 

 formed the lowest part of a very much thicker series of rocks, whose 

 higher portion is now entirely absent through denudation effected 

 prior to the Caledonian Old Red period ; and I still think that these 

 missing rocks may have included a band of marine limestone closely 

 resembling the Devonian Limestone, as this is seen at Plymouth, 

 due to a temporary return from continental to marine conditions. 



At any rate, and however this may have been, these Lanarkian 

 Eocks, which are certainly posterior in age to the Ludlow Rocks, 



