333 GEOLOGY OF BUTE. 



the line of the Crinan Canal. But then, as now, the moun- 

 tains of Arran and the Gowal district formed a great outer 

 barrier against the access of the ocean. Thus, throughout 

 all the inner waters of the frith of that time, conditions 

 existed favourable to the development of beds of fine sedi- 

 ment which the stormy waters and tidal currents, sweeping 

 the south coast of Arran, would not allow to settle down 

 over the surface of the boulder-clay when the land was 

 sinking. The origin of this stoueless clay is very difficult to 

 understand. Its close resemblance to glacial mud must 

 strike every one who has examined the deposits in the quiet 

 bays on the lake of Brienz. We have already traced, in 

 speaking of the Arran drifts, the probable origin of the other 

 beds; the origin of the laminated clay is now the most 

 difficult part of the problem. If deposited on the sea 

 bottom, by currents passing in from the outer ocean under 

 the frozen surface of the inner frith, the total absence of 

 fossils is difficult to understand, though the absence of stones 

 would be expkined ; whereas, if formed from mud drifted off 

 from the ends of glaciers by currents passing along shore, 

 or dropped from ice floating about in the unfrozen frith with 

 a load of earth and stones, the absence of stones from the 

 clay is equally difficult to explain. The fineness and perfect 

 lamination of the clay, and the total absence of sand and 

 gravel, indicate a slow and tranquil deposit, far out from the 

 shore, in a deep sea with access to the ocean, but either 

 frozen over or free from floating ice. We cannot suppose 

 it so deep that no shells could exist, since we know there 

 is life at all depths, and that an enormous elevation of the 

 bottom took place before the deposit of the Arctic shell bed 

 began over it. Difficulties, indeed, beset every supposi- 

 tion regarding its origin : it cannot yet be positively affirmed 

 that it is not really a terrestrial and not a marine formation ; 

 and we can only wait for more extended observation of the 

 conditions under which it is associated with the other beds, 

 and a strict definition of its geographical limits. We shall 



