Sir H. JEL. Soioorth — Geological History of the Baltic. 553 



passing tidal wave depositing its burden. This evidence is, however, 

 at first sight difficult to equate with the experimental evidence 

 based on investigations specially directed to test whether the land 

 has been and is now rising gradually from the sea. On this latter 

 issue a very large and divergent testimony is available, for the 

 polemic has now lasted for nearly two centuries, since Celsius 

 wrote bis well-known memoir in the Transactions of the Stockholm 

 Academy. 



There can be no doubt that, as in the case of all inland seas 

 into which a large number of rivers laden with sediment are 

 perpetually pouring, the accretion of sedimentary matters in the 

 Baltic, especially its northern part, is causing not only a shallowing 

 of its waters, but a great advance of the shore-line, which has gained 

 enormously in consequence. Thus, as Lyell urges, it was pointed 

 out by the opponents of Celsius that by the process of delta-making 

 there had been a gain of half a mile in 45 years at Piteo, and of a mile 

 in 28 years at Luleo, both in the Gulf of Bothnia (" Principles," 

 12th ed., vol. ii, p. 182), This cause, as in so many places in England, 

 bas induced the shallowing of harbours and the presence of shells 

 far from the sea in the black clays forming a kind of delta 

 deposit in so many places, etc., etc., and no doubt many of tbe 

 alleged instances quoted to prove an actual rise of the land are 

 attributable to this quite different cause. Others are due to test 

 marks having been made on stranded boulders which have been 

 actually moved into shallower water, and thus giving misleading 

 evidence. 



Another misleading element is the extreme variation in the normal 

 level of the Baltic watei*. Although there is no actual tide in that 

 sea, there are other notable causes of variation in its level. It 

 has been ascertained that the great differences sometimes occurring 

 in barometrical pressure cause a corresponding differential change 

 of several feet in different parts of the sea. A similar effect is 

 induced by the variation in the amount of fresh, and therefore light, 

 water and of salt water, which causes a change between the Summer 

 and Winter level of the sea in different parts, and, in fact, its 

 level in the upper parts of the Bothnian Gulf has been ex- 

 perimentally shown by Mr. Wolfstedt to vary as much as 18 feet 

 from that of its southern parts, and it no doubt again varies 

 greatly according to whether the rivers and upper parts of the 

 Bothnian Gulf are frozen or free. 



This variation qualifies immensely the value of various ex- 

 periments which have been made at different times by putting 

 marks on exposed rocks, etc., at the sea-level and then examining 

 them some years afterwards to see what changes have occurred. 

 There is a double ambiguity in the process, one dependent on the 

 controlling conditions of level when the mark was made, and tbe 

 other on the similar conditions when it was afterwards examined. 

 Hence the different and inconsistent results which bave been 

 drawn from this kind of evidence, and I am bound to say that 

 Lord Selkirk's careful examination of the problem on the spot 



