238 TRANSACTIONS, NATURAL HISTORT SOCIETY OF GLASGOW. 



larians, occasionally showing the double test, often abundant, and 

 sometimes with the spines attached ; and particles, some of them 

 vesicular, and probably of both volcanic and cosmical origin, 

 the vermilion specks abounding at parts, probably oxidised 

 globules of meteoric iron, forming an exceedingly lieautiful object 

 for the microscope, and resembling, when spotted ever the surface 

 of a pale-green shale, a refined variety of a v'erd antique. 



It has been suggested that these red and green shales were 

 deposited in very deep parts of the oceans of Arenig time, 

 and are represented at the present day by deposits of similar 

 colour and fineness of material taking place in the deepest 

 parts of the present oceans. 



From the examination I have made I think the red shales 

 have been deposited in the lowest depths. This is not made 

 out by the microscope, but by logic, there being two beds of 

 green shale to one of red. I take this to mean that when the 

 ocean bed (by subsidence) had reached a certain depth — not 

 by any means a given number of fathoms from the surface — 

 green sediment was deposited; when it reached its greatest 

 depth, red shale was laid down; when it again rose to its first 

 depth, green shale was again accumulated. In one locality I 

 examined there was a beautiful set of " passage beds," reddish 

 and greenish bands alternating for a few feet. 



Radiolarian Chert-shales. — The Radiolarian chert-shales are 

 exceedingly fine-grained, but even in this respect they vary, some 

 of them containing a little mica, evidently derivative, and also 

 occasionally mica which has apparently been developed in them 

 by dynamic metamoriihism since their formation, this having 

 been brought about by pressure or squeezing when the strata 

 were being turned up on edge, and abundance of minute irregular 

 flakes may often be seen on slickensided surfaces, sometimes 

 called shorn or flaser structure. The structure called flaser und 

 augen is also commonly seen under the microscope in examining 

 those shales, and has been caused by Radiolarians or other 

 minute hard bodies which happened to be in a zone of shearing. 

 More rarely one comes across perfect hexagons of secondary 

 mica, in little clusters, the individual plates or crystals being 

 sometimes as much as '4 of a mm. in size. The chert-shales 

 also contain minute particles of magnetite, often congregated 



