396 SCIENCE PROGRESS 



carried into the East of Scotland, where he demonstrates, on 

 lithological and palaeontological grounds, the continuity of all 

 the horizons delimited in the west. The two lowermost, 

 however, are not typically developed owing to the prevalence 

 of estuarine oil-shale conditions of deposition over the eastern 

 area during that period. 



The discovery of plant-bearing cherts in the Old Red 

 Sandstone of Rhynie, Aberdeenshire, by D. W. Mackie of 

 Elgin, is of more than ordinary importance to both geologists 

 and palaeobotanists. The plants have their structures perfectly 

 preserved, and Drs. Kidston and Lang have made the utmost 

 use of this unique opportunity of studying the microstructure 

 of plants of this early age. They have separated a new class, 

 Psilophy tales, to include Rhynia and certain of the species col- 

 lected under the name of Psilophyton princeps. Dr. Home 

 explains the geological import of this discovery. The Rhynia 

 occurs in the position of growth, and no less than six peat-beds 

 are to be distinguished within the eight feet of chert. The 

 geological bearing of the occurrence of these land plants upon 

 the hypothesis of the fluviatile origin of the Old Red Sandstone 

 is obvious (see Science Progress, October 191 7, p. 333). 



Reed's work on the brachiopod fauna of the Ordovician and 

 Silurian rocks of Girvan emphasises the American characters of 

 the fauna of the Stinchar limestone and of the Balclatchie Beds 

 (Ordovician) ; but these traits are lost in the succeeding beds, 

 and in the Silurian, in which the European facies is practically 

 unmixed with foreign elements. The predominance of local 

 and peculiar species is a distinctive feature, and suggests a con- 

 siderable degree of isolation of the Girvan area during Lower 

 Palaeozoic times. 



Grabau recognises three main centres of Lower Ordovician 

 sedimentation in western Europe, a Baltic and a Mediterranean 

 area, separated by the great peninsula of Armorica, and both 

 communicating with the Ordovician Atlantic. The third area, 

 North Scotland and Western Scandinavia, was entirely separated 

 from the Atlantic by the old Caledonian land mass which 

 extended across to Newfoundland. The arrangement and 

 succession of the early Ordovician rocks indicate an eastward 

 advance of the Atlantic waters, with a concomitant lateral 

 spreading and inundation upon the shores of Armorica and 

 Caledonia. A second great event was the retreat of the late 



