240 TRANSACTIONS, NATURAL HISTORT SOCIETY OF GLASGOW. 



badoes and the Nioobar Islands — the Radiolaiians in the deposits 

 of which are so fresh as to resemble recent species, and are 

 supposed to be of Tertiary age. 



Not long ago it was thought that the rocks contained no 

 organisms which had lived in great depths of ocean, and this 

 led to the theory of the permanence of ocean basins during all 

 geological time; but the finding of Radiolarians in four great 

 systems — the Silurian, Devonian, Carboniferous, and Tertiary — 

 has exploded that theory, and shown us how pliable the earth's 

 crust has been in times even so recent as the Tertiary period. 



So far as I know, no organisms but Radiolarians have been 

 hitherto recorded from the Arenig-Llandeilo chert-shales. Some 

 of these shales I found to be pretty free from Radiolarians, 

 other parts were crowded with them, and some have carious 

 hollows which very likely represent them. In fact, this is 

 placed beyond conjecture when we find occasional spines spring- 

 ing from their sides, the double test often remaining. 



In the list of Radiolarians from the Southern Uplands given 

 by the officers of the Geological Survey,* the species from the 

 Arenig cherts have all been found in the Llandeilo cherts, so 

 that the Radiolarians are useless as " zonal fossils." It appears 

 to be different, however, with the Conodonts, as, from an 

 examination of about sixty bands of the shale between the 

 chert-layers of Hunt Law Cleuch, I found Conodonts in every 

 band. On the other hand, in the fine section in the bed of 

 the Wanlock Water, seventeen yards north-west of the mouth 

 of Rea Burn, I only got one Conodont, and it is different from 

 all the rest I found. The shale here is of a fine fresh green 

 colour, probably caused by silicate of iron. This was the only 

 chert-shale in which I found hingeless Brachiopods ; it is bounded 

 on the north-west side by a bed of much-crushed black shale, 

 and on the south-east by bluish shale, coarse-looking under the 

 microscope, with much mica, and containing no fossils. 



The fine cliff-section of chert-shale at Bennane Cave, north of 

 Ballantrae, has some shale with similar physical properties and 

 identical appearance under the microscope to the Wanlock Water 

 chert-shale, and from it I was equally unsuccessful in finding 



* Geo. Sur. Mem. Siliirian-Boeks of Britain (Scot. ), page 667, 



