June 7, 1SS8] 



NATURE 



127 



THE GEOLOGICAL STRUCTURE OF SCANDI- 

 NA VIA AND THE SCOTTISH HIGHLANDS. 



THE obvious connection and analogy between the 

 A geological structure of the crystalline rocks of the 

 Highlands of Scotland and those of Scandinavia have long 

 ■engaged the attention of geologists. Among the northern 

 observers to whose labours we are largely indebted for 

 our knowledge of the Scandinavian regions, D>\ A. E. 

 Tornebohm has proved himself a keen and indefatigable 

 explorer of the Swedish uplands. Many years ago he 

 showed that above clay-slates and limestones, with re- 

 cognizable Silurian fossils, there lies a great thickness of 

 quartzites, gneisses, and schists, called by him the Seve 

 group. In more recently studying the relations of these 

 rock-masses, he encountered some great difficulties, of 

 which he sent me at the time an account. I 

 could not pretend to solve them, but suggested, as 

 at least a working hypothesis, that the Scandinavian 

 structure might be fundamentally similar to that now 

 recognized as characteristic of the North-West High- 

 lands, where the apparent conformable superposition 

 of a series of schists upon fossiliferous Lower Silurian 

 strata has been produced by great terrestrial displace- 

 ments, whereby the overlying rocks have been crushed 

 and deformed, until they have assumed a new crystalline 

 structure along the planes of movement, these stupendous 

 changes having occurred at some time subsequent to the 

 Lower Silurian period. I have recently received from 

 Dr. Tornebohm the following letter, which he gives me 

 leave to publish, and which will no doubt be read with 

 interest by those who are aware of the recent progress of 

 research in this subject :— " It will perhaps interest you 

 to learn that your suggestion four years ago regarding the 

 construction of our Scandinavian^?/^ has turned out to 

 be correct, at least in my opinion. My late researches 

 have little by little driven me to the conclusion that the 

 crystalline schists belonging to what I have called the 

 * Seve group ' have been placed over Silurian strata by 

 an enormous eastward thrust. I admit that I have most 

 reluctantly come to this conclusion, knowing that it 

 implied a horizontal thrust of enormous masses of rock 

 for more than 100 kilometres. Such a stupendous move- 

 ment of entire mountain-regions is hard to realize ; but 

 facts are stubborn things." 



It will be observed that Dr. Tornebohm speaks of the 

 movement having been towards the east, whereas in the 

 north-west of Scotland it has been in the opposite direc- 

 tion. In a more recent letter, in reply to one in which I 

 had called his attention to this difference, he says : — 

 " Though in Scotland the great thrusts are westward, in 

 Scandinavia it is quite the reverse. Here the chief 

 movement has been to the east or south-east. In the 

 region of Trondhjem, indeed, there have been lesser 

 movements towards the north-west, but these may 

 have taken place somewhat later. At least I rather 

 suspect this, but am not prepared positively to affirm it." 

 I may remark that in Scotland also there are districts 

 where the thrusts have not come from the normal direc- 

 tion but from the westward. In the Island of Islay, for 

 example, I recently found the limestones and quartzites 

 piled up by sharply-cut thrust-planes which had a general 

 westward inclination at lower angles than the displaced 

 strata. One of the great problems in working out the 

 complicated geology of the Highlands is the determina- 

 tion of the positions and extent of such thrust- planes, and 

 the direction in which the displaced rock-masses have 

 been moved. There can be little doubt that much mutual 

 help in this research will be gained by a co-operation 

 between the field geologists who are engaged in the study 

 of these problems in Scotland and in Scandinavia. 



Arch. Geikik. 



TIMBER, AND SOME OF ITS DISEASES. 1 

 VIII. 



'T'HERE is a large and important class of diseases of 

 ■*■ standing timber which start from the cortex and 

 cambium so obviously that foresters and horticulturists, 

 struck with the external symptoms, almost invariably term 

 them " diseases of the bark " ; and since most of them 

 lead to the production of malformations and excrescences, 

 often with outflowing of resinous and other fluids, a sort 

 of rough superficial analogy to certain animal diseases has 

 been supposed, and such terms as " canker," " cancer," 

 and so forth, have been applied to them. 



Confining our attention to the most common and 

 typical cases, the following general statements may be . 

 made about these diseases. They usually result from im- 

 perfect healing of small wounds, the exposed cortex and 

 cambium being attacked by some parasitic or semi- 

 parasitic fungus, as it tries to heal over the wound. The 

 local disturbances in growth kept up by the mycelium 



Cam. 



Fig. 28. — Piece of tree stem affected with " canker." The injury commenced 

 after the two inner zones of wood (i and 2) had been developed : it extended 

 further in successive periods of growih, as shown by the receding zones 

 3, 4, 5, and 6, until all the cambium and cortex was destroyed except the 

 pieces D to D. Cam, cambium ; Cor, living cortex ; D D, dead tissues. 

 At each period of growth the attempt has been made to heal over the 

 wound, as shown by the successively receding lips. 



feeding on the contents of the cells of these tissues lead 

 to the irregular growths and hypertrophies referred to ; 

 the wounds are kept open and "sore," or even extended, and 

 there is hardly any limit to the possibilities of damage 

 to the timber thus exposed to a multitude of dangers. 



In Fig. 28 is represented a portion of a tree stem 

 affected with " canker " : the transverse section shows 

 the periods of growth numbered i to 6 from within out- 

 wards. When the stem was younger, and the cambium 

 had already developed the zones marked i and 2, the 

 cortex suffered some injury near the base of the dead 

 twig, below the figure I. This injury was aggravated by 

 the ravages of fungus-m3celium, which penetrated to the 

 cambium and destroyed it over a small area : in conse- 

 quence of this, the next periodic zone of wood (marked 3) 

 is of course incomplete over the damaged area, and the 

 cortex and cambium strive to heal over the wound by lip- 

 like callus at the margins. The healing is prevented, 



1 Continued from p. m. 



