xxxii Proceedings of Royal Society of Edinburgh. 
The Maculloch, Dick-Lander, Milne-Home theory — the glen once 
the site of a lake ; (2) The Darwin, Nicol, E. Chambers theory — the 
terraces mark the level of an arm of the sea at three different 
periods ; and (3) The Agassiz, Buckland, (Mr) Jamieson theory — 
glacier lake the glacier, melting at three widely separated periods, 
left the marks of this in the terraces. 
Dr Brown approached the problem from a new (the biotic) point 
of view. That the deposits contain no shells was accounted for by 
Darwin alleging that the carbonic acid gas in the rain-water had 
destroyed the shells. Mr Brown, remembering that the so-called 
shells of diatoms, being siliceous, would not he destroyed by this 
gas, resolved to search for diatoms in the terrace deposits, and 
diatoms were found which Professor Dickie of Aberdeen, an 
acknowledged authority, identified as fresh-water species. This 
seemed to favour the first theory just mentioned. It might, indeed, 
be asked. Were the data sufficient to warrant the inference"? What- 
ever answer may be given, we are indebted to Mr Brown for the 
introduction of this new element into these discussions. 
1876. Perhaps Mr Brown is seen at his scientific best in the 
paper “ On the Old Eiver Terraces of the Earn and Teith, viewed 
in Connection with Certain Proofs of the Antiquity of Man,” read 
before the Society in the beginning of 1876, and printed in vol. xxvi. 
of the Transactions. Before noticing the leading characteristics 
of this paper, I may refer to the circumstances which led to it, and, 
specially, to the introduction of the speculative element in dealing 
with Physical Geology phenomena. In 1838 M. Boucher de Perthes, 
Abbeville, France, published his now well-known book, De la 
Creation., in which he expressed the belief that he would find 
traces of primeval man in the fluviatile gravels of the Somme. 
In 1846, in another work entitled De V Industrie Primitive, ou 
les Arts et leur Origine, he intimated that his anticipations had 
been fulfilled, and in 1847 his Antiquites Celtic et Antediluvienne 
appeared, giving great prominence to his discoveries in these 
river gravels. For years little or no interest was taken in his 
works. But about 1860 the attention of geologists, biologists, and 
archaeologists was fixed on them, and a great controversy arose, 
in which the giants of the time — Murchison, Lyell, Falconer, 
Carpenter, and others — were conspicuous. The crucial inquiry came 
