2l8 



NA rURE 



[January 5, 1893 



pouss^e." But they occurred on a much smaller scale, 

 and there was no reason why the phenomena should be 

 considered otherwise than as quite exceptional. To 

 recognize the generality of that class of stratigraphical 

 accidents was a conquest of a high order, not only for 

 Scottish geology, but for all countries where the work of 

 orogenetic disturbances has for a long time suffered from 

 the agencies of erosion. The Highlands of Scotland 

 belong to that part of the old European continent which 

 in earlier Palaeozoic times emerged from the sea. Near 

 the end of the Silurian period it was subjected to enormous 

 pressure, which resulted in folding and breaking the 

 whole border of the dry land, raising in the air a series of 

 high mountainous ridges, the Caledonian chain of M. 

 Suess. But millions of years have since passed over the 

 land, and the continued action of atmospheric powers has 

 left but a very small part of the original mass. It is ex- 

 tremely difficult, therefore, to restore the broken continuity; 

 and throughthe quiet appearance of the now planed ground, 

 the geologist is everywhere bound to search after the 

 scattered signs of previous plication and fracture. This is 

 now the task to be fulfilled by the detailed Survey, and 

 every stratigraphical difficulty has to be treated in the 

 newly-acquired light. 



A few years after that discovery had been made in 

 Scotland, Prof. Marcel Bertrand made in Southern France 

 quite similar observations, showing that very limited 

 patches of older formations, which had been till then re- 

 garded as remnants of ancient islets, projecting out of 

 younger geological seas, were nothing else than outliers of 

 reversed folds, the remainder of which had disappeared 

 under the action of rain and rivers. 



In this manner the correction of a long accepted error 

 has led to stratigraphical conclusions of the highest im- 

 port. In the meantime these gigantic displacements 

 showed themselves accompanied by intense modifications 

 of the rocks, so that Geikie was entitled to write : " In 

 exchange for this abandoned belief, we are presented 

 with startling new evidence of regional metamorphism on 

 a colossal scale, and are admitted some way into the 

 secret of the processes whereby it has been produced." 



This is not the only occasion on which Sir Archibald 

 has given proof of his readiness to admit frankly and 

 decidedly the correction of opinions which have long been 

 held. Some years ago, when the Lower Cambrian fauna 

 had been detected by the officers of the Survey much 

 below the Durness limestone of the Highlands, in a series 

 of strata which rests unconformably on the Torridon 

 sandstone, he was the first to announce the fact before 

 the Geological Society. The " Precambrian," which he had 

 till then been rather reluctant to recognize, has now taken 

 its place in the scale of divisions. Moreover, he has 

 created a new name, that of " Dalradian," for the long 

 strip of Precambrian deposits which extends from Donegal 

 to the centre and south-west of Scotland. 



As one of the most characteristic formations in Scot- 

 land is the Old Red Sandstone, we cannot be surprised 

 that Sir Archibald has devoted much care to the de- 

 scription of the peculiarities of that interesting group of 

 strata. After a long and detailed study of the whole 

 ground, he has summed up his views in some important 

 memoirs, published in the Transactions of the Royal So- 

 ciety of Edinburgh. There he has called again to life the 

 NO. I 2 10, VOL. 47] 



old and long-extinct lakes, where the grits and con- 

 glomerates of the Old Red were piled up through the 

 disintegration of surrounding formations, namely, Lake 

 Orcadie, Lake Caledonia, Lake Cheviot, Welsh Lake, 

 and Lake of Lome ; each of them being a separate basin, 

 where the work of sedimentation has been many times 

 interrupted by volcanic outbursts, while in the adjacent 

 and more quiet seas there were accumulated the marine 

 deposits of Devonshire. 



But the chief work of Sir Archibald seems to be his 

 exhaustive review of the volcanic history of the British 

 Isles. While his brother, Dr. James Geikie, the author 

 of "The Great Ice Age," has done excellent service by 

 deciphering the marks of former ice action on the soil of 

 the United Kingdom, Sir Archibald has been particularly 

 attracted by the work of fire, i.e. by the records of that 

 volcanic activity, the evidence of which is so deeply im- 

 pressed on the scenery iof the Hebrides, of Wales, and 

 other districts of Great Britain. 



The British Isles are now a very quiet ground, where 

 explosive activity and projection of stones seem to be 

 restricted to electoral periods ; and although Scotland has 

 been from time to time shaken by minor earthquakes, no 

 human eye has ever seen there any volcanic outburst. 

 Nevertheless, during Tertiary times, immense sheets of 

 lava were poured out in the north-west of the country. 

 To discern the site of the centres of eruption, and deter- 

 mine the old chimneys, the remnants of which give a 

 glimpse into the lowest parts of ascending lavas; to 

 discriminate the volcanic necks., the intrusive sheets and 

 dykes, the bedded lavas and the tuffs — this was the first 

 part of the task undertaken by Sir Archibald. But it 

 was not enough for him to re-ascend in the past to the 

 beginning of the Tertiary period. Not only in the Old 

 Red of Scotland, but in the very heart of the oldest forma- 

 tions known in England and Wales, there were numerous 

 evidences of previous volcanic activity. To use Geikie's 

 words : " Placed on the edge of a continent and the 

 margin of a great ocean-basin, the site of Britain has lain 

 along that critical border-zone where volcanic energy is 

 more active and continuous." 



The chief outlines of that marvellous story, which was 

 hardly suspected some years ago, were recently traced 

 in Geikie's presidential addresses to the Geological So- 

 ciety of London ; a work which has been qualified by Mr. 

 Iddings, the distinguished American petrographer, as 

 " one of the most important contributions to the history 

 of volcanic action." Nevertheless, it is only a preliminary 

 paper, and in the same manner as he already has devoted 

 a special memoir to the volcanic outbursts of Tertiary 

 times. Sir Archibald promises to publish in a short time 

 a detailed account of the Palseozoic eruptions. 



In order to become competent for such an under- 

 taking, the author had prepared himself without sparing 

 time, labour, or trouble. Having travelled over much 

 of Europe, from the north of Norway to the Lipari 

 Islands, he was anxious to learn from personal observa- 

 tion the broad features of that American continent, the 

 geological construction of which seems to have been 

 conceived on a much larger scale than that of Europe. 

 Therefore in 1878 he rambled over many hundreds of 

 miles in Western America, from the Archaean fields of 

 Canada to the huge volcanic plateaux of Oregon and 



