Nature Vol. 294 5 November 1981 13 of the river's development. Palaeo­ obtained for certain levels, but the settlement at Biskupin near Bydgoszcz. botanical evidence (from macroremains, sediments are calcareous, making the Built upon a low-lying peninsula extending such as fruits and seeds, and from pollen) is precise interpretation of such dates into a 100 hectare lake this timber-built also helpful and has been analysed by K. difficult. It is reasonable, however, to settlement, dating from 550 BC, has been Tobolski (University of Poznan). conclude that the development of the wider extraordinarily well preserved as a The outer, larger series of palaeo­ series of meanders (which replaced the consequence of raised lake levels swamping meanders contains botanical evidence of braided system) occurred during the late­ the wooden foundations. 35,000 stakes of an origin during the closing phases of the glacial. This could be accounted for by the oak and pine formed a palisade around the last glaciation. The pollen spectra are herb reduced flow resulting from the camp, which covered an area of about 2 dominated and the major tree components completion of ice wastage, the hectares and within which were rows of are birch and pine. The dwarf birch (Betula development of a complete (and partly wooden buildings, over 100 in all. The nana), juniper, Artemisia and wooded) vegetation cover, and the population was largely agricultural, Chenopodiaceae all provide evidence possibility of reduced precipitation. growing wheat, barley, millet, beans, suggestive of open, park-tundra vegetation The inner series of meanders proved to lentils and flax, and this arable emphasis, typifying late-glacial conditions. Precise be considerably younger. The pollen coupled with the timber necessary to build location of the sediments within the late­ spectra of the basal sediments within these such a construction, must have involved glacial chronology is difficult, on the are tree dominated, with oak predominant. extensive deforestation of the surrounding palaeobotanical evidence, and one Available radio-carbon dates suggest that region. Which brings one back to the wonders whether the argument about some of these younger palaeomeanders question of whether such forest clearance whether the basal deposits date from began forming around 4,000 years ago, and could have affected the hydrological before or after the B¢>11ing Interstadial can some later than this. The smaller radii regime in such a way as to lead to raised ever be resolved on this basis. The observed suggest that more water was moving down lake levels and the ultimate swamping of changes in sediment and pollen the Warta, but whether this was a the settlement which finally led to its stratigraphy could so easily be a consequence of climatic changes or human abandonment. Since this particular period consequence of in wash from the steep sides deforestation is impossible to ascertain. in prehistory is generally believed to have of the channels, thus confusing the The enigma of man's role in the been a time of increasing precipitation and stratification of the deposits. palaeohydrology of central Poland is lowered temperatures in northern Europe, Radiocarbon dating has been attempted perhaps epitomized by the remarkable this may have to remain just another and figures in excess of II ,000 BP have been excavations of an Iron Age fortified palaeohydrological conundrum. D Once the possibility of a nuclear A particularly anomalous Seyfert galaxy origin for this gas is admitted, many from J.H. Krolik kinetic energy - 2 x 105s n; 1 erg, where other questions instantly arise. Why did 3 SEYFERT GALAXIES and their quasar ne is its electron density in cm· • Such a the expulsion last only for 106 years (its cousins have providect much observa­ large mass of gas moving at such high kinematic age)? Seyfert galaxies are tional mash for the vats of theoretical speed has never been seen elsewhere. generally supposed to live at least lOS speculation over the years since their The first question that comes to mind years. Why did it occur only in discovery. A recent article by T. is the source of ionization to drive the Markarian 335, a galaxy which doesn't Heckman and B. Balick 1 has thrown an Ha recombination radiation. Heckman appear remarkable in any other way especially juicy bucketful into this and Balick check that it is plausible for (but one, which we discuss in the already potent brew. Ordinarily, what the Seyfert nucleus to be supplying following paragraph). In their kilo­ astronomers find extraordinary in these enough ionizing photons. Baldwin and parsecs-long passage out into the objects are the very large continuum colleagues2 previously showed that the galaxy, why haven't the clouds been luminosity (1043 -1045 erg s- 1 in Seyferts, nucleus of 3C 120 superionizes its H 11 appreciably slowed by drag? Why is the 1045-!()47 erg s- 1 in quasars) and the very regions. Here the Seyfert nucleus has a shape of the nebula so strongly strong, broad (I Q3 -I ()4 km s- 1) emission much more dramatic influence on its asymmetric? lines coming from an optically galactic environment. The final, and perhaps most unresolved source believed to be no The second question is the source of interesting, question stems from more than a few parsecs in size. In this the gas. An obvious supposition, and Heckman and Balick's measurement of new paper, attention is turned to extra­ one that Heckman and Balick consider, the radial profile of the galaxy's ordinary goings-on outside the nucleus is that this gas is material that once continuum emission. They find that the of a Seyfert galaxy. radiated the nuclear broad emission surface brightness declines away from Heckman and Balick made vidicon lines but has now spread further out the centre in a way more characteristic pictures of the galaxy Markarian 335 into the galaxy. Unfortunately, we have of elliptical galaxies than spirals. If with a series of interference filters no clear way of telling whether the Markarian 335 is an elliptical galaxy, it covering bands centred on Ha and [0 nuclear emission line clouds travel would be the only such Seyfert galaxy III]A5007, each 3,300 km s 1 wide radially in, radially out, or go in any known; all other Seyfert galaxies whose (FWHM), and extending in total over a other direction. Some lines (for types have been determined are spirals. range ±5,000 km s· 1 from line centre. example, C IV A\549) have profiles Ordinarily, when an elliptical galaxy has Most of the line emission does indeed which are easy to measure, but are a line-emitting nucleus, it is also a bright come from the galactic nucleus, but emitted isotropically, and so tell us radio source, which Markarian 335 is surprisingly, there is a significant flux in nothing about cloud kinematics. On the certainly not. On the other hand, most of the observed wavelength range other hand, those lines, such as La, Seyfert galaxies sometimes do evince from regions clearly separate from the which are emitted only from one face of small-scale radio emission near their 3 nucleus. Interpreting the emission as a cloud are often so distorted by cores4 • VLA observations of this coming from a large photoionized blending or intervening absorption that unusual Seyfert galaxy might be a par­ nebula, the inferred mass of gas outside their usefulness is destroyed. Therefore, ticulary fruitful next set. n the nucleus is - 2 x wx n. 1 M 'lnd its the presence of this gas may be as good ~ l;') an indication that at least some Seyfert I He12kman & Balick, B. Aslruphys. J. 247,32 ( 1981). 2. Baldwin et al. Asrrophys J. 236, 388 (1980). J.H. Kro/ik is in the Harvard Center for nuclei expel gas some of the time as asym­ Kwan & Krolik Aslrophys. I (in the press). Asrrophysics, Cambridge, Massachusetts. metry of nuclear emission line profiles. Wilson & Willis Astrophys. J. 240, 429 ( 19RO). 0028-0836/81 I 450013-03$01.00 ©1981 Macmillan Journals ltd .