258 Proceedings of the Royal Physical Society. 
similar rythmic cycles of deposition, though few traces of land surfaces are 
recorded. 
NEBRASKAN FAUNA. 
While the revision of the Lothian and Stirlingshire Coal-fields by the 
Geological Survey was proceeding, Mr D. Tait discovered that the dark shales 
and the cementstone bands held a pecular, and to him, unfamiliar facies of 
lamellibranchs, brachiopods and gasteropods. These were submitted to 
Dr Wheelton Hind, who showed that this facies, although it was unknown in 
Britain, had already been described from the Coal Measures of Nebraska and 
Illinois, in North America, In 1905 he gave the first preliminary notice of 
the discovery, and in 1908 he described the lamellibranchs and gasteropods 
before the Royal Society of Edinburgh. Some of the lamellibranchs were 
known to occur in Permo-Carboniferous rocks in Russia, and at first 
it was thought that the find was that. of a colony caught in the act of 
migration from America to Europe. Against this view, however, is the 
fact that the late James Thomson of Glasgow had recorded some of the 
forms as occurring in the lower limestones of Tirfergus Glen near Campbeltown. 
Later discovery of some of the forms in the Index Limestone position 
found in cores of bores put down in the Carse of Stirling, from the 
Calciferous Sandstone Series at Arbigland by Mr John Smith, and from the 
Lower Limestone Group in Fife by Mr James Wright, of Kirkcaldy, tend to 
show that they must have been permanent somewhere near our area and 
only occasionally migrated into it as conditions became favourable. One 
point, however, is strongly brought out by this discovery, that the forms 
must have been dispersed along shore lines which extended from European 
tussia to America across what is now the Atlantic Ocean. 
The peculiar assemblage of fossils that characterise Dr Hind’s Pendleside 
group, and which, he thinks, marks a distinctive zone somewhere about the 
horizon of the Millstone Grit, have been found at much lower horizons in 
the West of Scotland. Some of these are recorded by Mr J. Neilson from the 
Orchard Limestone, one of the Upper Limestone Group, and also from the 
Calderwood Cement, belonging to the Lower Limestone Group, enclosed in 
sediments similar to that in which they are embedded in Dr Hind’s type 
area. Mr James Wright of Kirkcaldy records Posidonomya becheri, one of 
the characteristic Pendleside forms, from a still lower horizon in Fife, 
viz. that of the Abden Limestones. These facts seem also to show that 
the assemblage is one which naturally associates itself with some particular 
type of sedimentation where, if accumulation is just keeping pace with 
depression, it may continue to live on; but is ousted from areas where 
