Dr. J. W. Gregory — Moine Pebbles. 



447 



in its proximal region : thus the humerus is still quite recognizably- 

 Crocodilian, while that of Geosaurus, figured by Fraas, is not. In 

 the case of the radius, and more particularly the ulna, there are still 

 traces of their condition as long bones, while in Geosaurus this is not 

 the case. The carpals and metacarpal are similar in both genera, 

 but the phalanges seem to have undergone most reduction in 

 Metriorhynchus. 



In most reptiles in which the fore-limb has become paddle-like 

 it tends also to become larger, this enlargement being frequently 

 accompanied by additions to the number of bones composing it. Thus, 

 not only is it usual for the number of phalanges to be increased, 

 sometimes very greatly, but additional elements may appear in the 

 carpal region, e.g. in Tricleidus. In Metriorhynchus, on the other 

 hand, the paddle-like modification was acquired while the limb was 

 undergoing reduction, and in this case the number of elements has 

 been much reduced, the phalanges having nearly, and the distal 

 carpals entirely disappeared. The limb had already become so small 

 that it can have been of little use in swimming or even in balancing. 



Some dimensions (in millimetres) of this paddle are given below: — 



Humerus : length 



width of upper end . 

 width at deltoid crest 

 width at distal end 

 Radius : greatest length 

 greatest width 

 Ulna : greatest length 

 greatest width 

 Eadiale : greatest length 

 greatest width 

 Ulnare : greatest length 

 greatest width 

 Length of metacarpal I 

 II 

 III 

 IV 

 V 



(appr 



(appri 



67 

 21 



ox.) 27 

 15 

 22 

 26 

 26 

 15 

 19 

 15 

 14 

 12 



ox.) 19 

 23 

 26 

 22 

 21 



The two cbracoids and the left scapula are also preserved, but they 

 do not seem to differ in any marked respect from specimens described 

 in the Catalogue. 



1 



IV. — Moine Pebblks in Torridonian Conglomerates. 



By J. W. Gregory, D.Sc, F.R.S. 



1HE relation of the Torridon Sandstone to the Moine Gneiss or 

 Eastern Schists' is one of the primary questions in the 

 geology of the Scottish Highlands. These two widespread series of 

 rocks occur on opposite sides of the great overthrusts in North- 

 Western Scotland ; and another remarkable feature of their distribution 

 is that though the Torridon Sandstone often rests directly upon the 

 Lewisian Gneiss, it never occurs on the Moine Gneiss. The view has 

 therefore been suggested that the Moine rocks are the eastern 

 metamorphosed continuation of the Torridonian. Some altered 

 Torridon Sandstones certainly resemble the rocks of the Moine Series. 



