352 ON GEOLOGICAL NOMENCLATUKE. 



different colours. There are nine of these bands, corresponding 

 with the chief periods into which he divides the geological scale. 

 These are the colours used by the Swiss Geological Commission, 

 which is a body charged by the Federal Government with the 

 execution of the geological map of Switzerland ; and, therefore, as 

 the table is designed, of course, primarily for his own countrymen, 

 the compiler could not have done better than adopt the colours of 

 the national map. JN'ow Professor Renevier is one of the workers . 

 of the Federal survey and has just finished a sheet of part of the 

 "Western Alps, which will be a great boon to the visitors to the Bex 

 Diablercts and Gruyere districts. He very justly remarks, there- 

 fore, that keeping the same conventional colours for both will much 

 conduce to the rapid understanding of the maps. But he is perhaps 

 a little sanguine in thinking that these colours are likely to be 

 adopted by other nations. Of course, as the colours have been 

 settled upon by the Federal Commission after, no doubt, mature 

 consideration, we cannot presume to criticize them. Most of the 

 colours of the English Geological Survey are, I think, admirably 

 chosen, indicating very often the colour of the chief groups of beds 

 themselves; e.g., the Cretaceous with us is represented by 

 various shades of green ; it includes a great thickness of Greensand, 

 and the Gault clay, which is a greenish blue ; so are some 

 of the Wealden beds. The Oolites are on our maps tinted yellow 

 in different shades: this is the prevailing colour of the Jurassic 

 limestones with us. The Trias has a red colour, and very aptly 

 for that is the chief tint of our Few Red Sandstone and Bunter. 

 The Coal Measures we represent by a diluted black ; the Carbonif- 

 erous Limestone is coloured bright blue, but this gives rise to little 

 inconvenience Id practice, though a blue (a different shade, however) 

 is used by Limestone in the Silurians ; and absolute regularity of 

 shades is impossible, and very seldom do all the formations occur in 

 the same sheet. The Old Red Sandstone has a darker shade of red. 

 The Silurians are indicated by different shades of slate colour, the 

 idea no doubt being taken from the colour of N. "Wales roofing slates, 

 the best slates coming chiefly from these older Palaeozoic rocks. 



