52 Mr. C. W. Peach on Nature-Printing of Sea-weeds, 



be eaten away by its overlying corrosive brother. The impress 

 is thus made, and the stone, when washed by the next flowing 

 tide, is cleared of all the vegetable matter, both of the decaying 

 Desmarestia and dissolved Ralfsia ; the picture is then beauti- 

 fully shown (fixed) on the light-yellow coated slab. Not only 

 does the Desmarestia destroy the Ralfsia, it also dissolves some 

 of the rock ; and thus, as well as the depression left by the 

 washing-out of the Alga, it is engraved in the stone ; and pro- 

 bably this depression is added to, time after time, by the carbonic 

 acid in the sea-water, and thus the more indelible it becomes. 



Even in rocks of a deep dark-grey colour, containing little or 

 no lime, and on which no growing Alga is to be seen, the Des- 

 marestia imprints its form, by extracting the colour ; and, al- 

 though not so distinct as the prepared one, it is often well 

 defined. I saw such on the coast ; and the lady of the Rev. 

 Mr. Learmonth kindly showed me one, which a quarryman had 

 brought, some years before, as a plant of the age of the Old Red 

 Sandstone; it retained all the markings fresh. These rocks dip 

 gently to the westward, and are exposed to the full sweep and 

 terrific lash of the waves of the Atlantic. 



The first, and I may say, only impress must be quickly done, for 

 each returningtide would certainly remove the weed, and leave not 

 a trace of the vegetable matter behind. When we take into con- 

 sideration the well-known property possessed by the Sporochnece 

 of destroying other Algse, we cease to wonder at the eating-away 

 of the Ralfsia ; the extraction of the colour and the dissolving the 

 hard rock will, however, cause some surprise, and we naturally 

 ask, what can this lithographic property be ? This and many 

 other questions must be passed, and the one uppermost attended 

 to; for we are looking back upon the ancient periods in the 

 history of our earth. I have seen, in most of our geological 

 formations, plant-like forms " painted," or rather, " discharged," 

 especially when cleaving the Devonian and Silurian rocks of 

 Cornwall and the Old Red Sandstones of Scotland, and have 

 been struck by their forms ; for so much like plants have they 

 appeared, that again and again have I found great difficulty in 

 persuading myself that they were not so, — always pleading the 

 absence of organic matter ; and this was a sad stumbling-block, 

 for not a vestige could be seen. Others have been equally per- 

 plexed. Our lamented friend Hugh Miller, after speaking of the 

 now acknowledged land-plants of the Lower Old Red Sandstone 

 of Caithness, at page 435 of the ' Testimony of the Rocks/ says, 

 " I may here mention, that curious markings, which have been 

 regarded as impressions made by vegetables that had themselves 

 disappeared, have been detected during the last twelvemonth in 

 a quarry of the Lower Old Red Sandstone near Huntley, by the 



