40 



the prevailing hue is nearly always red of some kind or other. We 

 have several such groups of red strata in the geological series — the 

 Old Red Sandstone, or a part of it, at all events, is a good example. 

 All these red rocks have certain peculiarities in common. I'hey 

 contain hardly any fossils, and the few they do contain are of 

 peculiar types. The rocks are red, not because they are made up 

 of grains that are red throughout, but because each separate com- 

 ponent grain is coated over with a film of peroxide of iron. Then, 

 again, they are all more or less associated with certain chemical 

 deposits either imperfectly-developed or wanting altogether in the 

 rocks that are not-red. Lastly, the fossils that occur in the not-red 

 strata, interstratified with the red deposits, are of a character quite 

 unlike that of the fossils we get from beds that all agree in regarding 

 as of marine origin. 



Many years ago Mr. Godwin Austin suggested that these red 

 strata may owe their exceptional character to their having been 

 accumulated in great inland lakes like the Caspian, the Dead Sea, 

 the Salt Lake, and others. Leaving the peculiar character of the 

 fossils out of sight, we do not know of any marine deposits in 

 process of formation at the present day wherein the component 

 grains are being coated with a film of peroxide of iron. On the 

 other hand, we do know of many lakes wherein a considerable 

 deposit of ferruginous matter, in one form or another, accumulates 

 in the course of even a year. In some of the Swedish lakes, for 

 instance, this annual accumulation takes place in quantities sufficient 

 to make it worth while to dredge the bottom of the lake period- 

 ically, merely for the sake of the iron ore. The iron is probably 

 brought into the lake in the form of the soluble carbonate of iron, 

 which is altered into the peroxide after deposition. Or it may arise 

 through organic agencies. At any rate, it is known to be in process 

 of deposition in inland lakes ; while it is not known to be forming 

 beneath the waters of the sea. 



But if we experience a difficulty in accounting for the deposition 

 of iron ore under ordinary marine conditions, the difficulty is greater 

 when we have to account for the deposits of gypsum. Under no 

 conditions we yet have any knowledge of could deposits of gypsum 



