154 THE HABITAT OF THE EURYPTERIDA 



i 



the material which filled up the mid-Scottish basin or "Lake 

 Caledonia," for it was hemmed in on the west by a narrow ring 

 of hills separating it from "Lake Lome" in North Argylshire, and 

 on the south by hills along an east-west line through the Firth of 

 Forth, and on the north by the Highlands which were the source of 

 the 1 6, coo feet of sediments deposited in Lake Orcadie, while to 

 the east the sea covered France. The only other source would 

 be a mountain chain in the present English Channel, but the ob- 

 jections to this are obvious. A natural question that arises often 

 in reading Geikie's monograph, and one which Macnair and Reid 

 most pertinently ask is how outliers of conglomerates on the tops of 

 high mountains, in the very regions which were supposed to have 

 been lake barriers, are to be accounted for. Geikie has proposed 

 that perhaps they represent old fiord-like indentations in the shore- 

 line. This explanation will not serve, however, when such outliers 

 are found on what must have been the very centre of the ridge between 

 Lakes Orcadie and Caledonia, such, for instance, as Macnair and Reid 

 mention at Mealfourvonie just north of Loch Ness in Inverness where 

 an outlier is found 2284 feet above sea-level, and at Tomintoul in 

 Banff, and Rhynie in Aberdeen. The outliers in all parts of Scotland 

 indicate that the deposit was essentially continuous, though varying 

 in lithological character and origin from place to place. 



(e) Structural features. The cross-bedding, ripple marks, and 

 other structural features that are cited by some authors as indicative 

 of marine littoral conditions of sedimentation, by others as lacustrine 

 littoral, will be considered below under the third theory of the origin 

 of the Old Red sandstone (p. 189). 



(2) Faunal. Attention should be called to certain erroneous lines 

 of argument that have been used and which fall down because based 

 on false premises. For instance, it is impossible to prove that the 

 Cld Red sandstone eurypterids were marine by saying that the 

 Siluric ones were and that therefore the Devonic ones of the same 

 genera must also be. First it must be proved that the Siluric euryp- 

 terids were marine. To quote once more from Macnair and Reid: 

 "We have .... seen no reason assigned why Eurypterids and 

 Placoderms of the same genera, which are marine in the late Upper 

 Silurian, and fishes of the same genera and species which are equally 

 marine in the Devonian of Russia and Central Europe, as well as in 

 the Devonian of North America, should be termed equivocally marine 

 in the Old Red sandstone" (160, 219). It may be remarked that the 



