of Edinburgh, Session 1873-74. 341 
understood from the preceding diagram representing the section 
just referred to. 
In searching for diatoms, it was necessary to avoid the bed a, 
which has been formed since the time of the parallel roads. It 
was thought safer also to throw out of view the bed 5, the upper 
surface of which is in contact with a. Attention was therefore con- 
fined to the beds c and d. The outside weathered portion of the 
bed was in each case removed, and part of the internal contents of 
the bed cut cleanly out — that from d being about 10 feet below the 
surface. The material thus obtained was washed in distilled water 
and microscopically examined. It was found that the search re- 
quired much patience. Diatoms were ascertained to be present 
scattered very rarely through the material, but at last a series of 
specimens were got. These were sent to Professor Dickie, of 
Aberdeen, one of our highest authorities in this department of 
natural history, and the following species were determined by 
him : — 
Pinnularia viridis. Diatoma vulgare. 
Himantidium undulatum. Surirella panduriformis ? 
Of these the first three were got from bed c, and the first two and 
the last from bed d. 
Now these are all freshwater species, and their evidence is 
strengthened by the fact that there is the entire absence of any 
marine diatom or other organism. This would indicate that it was 
an old freshwater lake which had these parallel roads for its margins. 
Freshwater diatoms might, indeed, have been brought down into it 
even if it had been a sea loch, but the important fact is, that while 
freshwater species are found, it has been impossible to detect a 
single trace of anything marine. 
It is indeed true that it is only a single locality which has been 
searched in this way, and it would be going too far to hold the 
results as at once conclusive. Enough, however, has been done to 
show that this method of approaching the solution of the problem 
deserves to be followed out. Search should be made at other 
points along these parallel roads where they are laid open. They 
have been a kind of battle-field fought over by rival theorists for 
the last fifty years, and it will be strange if all the time multitudes 
