May 15, 1S84] 



X. I TURE 



67 



the position of some of the Cretaceous deposits and the marked 

 mineral differences between these and the Jurassic seem (..indi- 

 cate disturbances during some part of the Neocomian, but I am 

 not aware of any marked trace of these over the central and 

 western areas. The mountain-making of the existing 

 from the later part of the Eocene. Beds of about the age of our 

 Bracklesham series now cap such summits as the Diablerets, or 

 help to form the mountain masses near the Todi, rising in the 

 Bifertenstock to a height of 11,300 feet above the sea. Still 

 there are signs that tlie sea was then shallowing and the epoch 

 of earth movements commencing. The Eocene deposits of Swit- 

 zerland include terrestrial and fluviatile as well as marine 

 remains. Beds of conglomerate occur, and even erratics of a 

 granite from an unknown locality, of such a size as to suggest the 

 aid of ice for their transport. For the present I prefer, for sake 

 of simplicity, to speak of the upraising of the Alps as though it 

 were the result of a few acts of compression, though I am by no 

 means sure that this is the case. Thus speaking we find that in 

 Miocene times a great mountain chain existed which covered 

 nearly the same ground as the present Alpine region of Mesozoic 

 and crystalline rocks. To the north, and probably to the south, 

 lay shallow seas, between which and the gates of the hills was 

 a level tract traversed by rivers, perhaps in part occupied by 

 lakes. Over this zone, a-, it slowly subsided — in correspond- 

 ence, probably, with the uplifting of the mountain land — were 

 deposited the pebble beds of the nagelflue and the sandstones of 

 ! he molasse. 



Then came another contraction of the earth's crust ; the solid 

 mountain core was no doubt compressed, uplifted, and thrust 

 over newer beds, but the region of the softer border land, at any 

 rate on the north, was apparently more affected, and the sub 

 alpine district of Switzerland was the result. I may here call 

 your attention to the fact that, whether as a consequence of this 

 or of subsequent movements, the Miocene beds occur on the 

 northern flank of the Alps at a much greater height above the 

 sea than on the southern, and have been much more upraised in 

 the central than in the western and eastern Alps. Further, 

 I letween the Lago Maggiore and the south of Saluzzo, Mesozoic 

 rocks are almost absent from the southern flank of the Alps, 

 and the Miocene beds are but slightly exposed and occupy a 

 comparatively lowland country. I think it therefore probable 

 that the second set of movements produced more effect on the 

 ( lerman than on the Italian side of the Alps, producing on the 

 latter a relative depression. In support of this we may remark 

 that the rivers which flow from the Alps towards the north or 

 the west, start, as a rule, very far back, so that the watershed 

 of the Alps is the crest of the third range recki ming from the 

 north, and the great flat basin of the Po is the receptacle for a 

 series of comparatively short mountain rivers. These also take 

 a fairly straight course to the gates of the hills, while the others 

 change not seldom from the lines of outcrop to the lines of dip 

 of the strata — a fact I think not without significance. To this 

 rule the valley of the Adige in the eastern region is an exception. 

 May not this be due to the remarkable series of minor flexures 

 indicated by the strike of the rocks (Mesozoic and earlier) 

 immediately to the west of it, which probably influences the 

 course of the Adda, and can, I think, be traced at intervals 

 along the chain as far as Dauphine? Be this as it may. it is 

 obvious that the generally uniform east-north-east to west-south- 

 west strike of the rocks which compass the Alpine chain is 

 materially modified as we proceed south of the Lake of Geneva, 

 changing rapidly in the neighbourhood of Grenoble from a 

 strike north-east to south-west, to one from north-west to south- 

 east. This subject, however, is too complicated to be followed 

 further on the present occasion. I will only add that the singular 

 trough-like upland valleys forming the upper parts of some of 

 the best-known ro: . for instance, the Maloya — which 



descend so gently to the north, and are cut off so abruptly on 

 the south, seem to me most readily explained as the remnants of 

 a comparatively disused drainage system of the Alps. 



It remains only to say a few words on the post-Tertiary history 

 of the Alps. We enter here upon a troubled sea of contro- 

 versy, upon which more than the time during which I have 

 spoken might easily be spent ; so you will perhaps allow me to 

 conclude with a simple expression of my own opinion, without 

 entering into the arguments. That the glaciers of the Alps were 

 once vastly greater than at the present time is beyond all dispute ; 

 they covered the fertile lowlands of Switzerland, they welled up 

 against the flanks of the Jura above Xeufchatel, they crept over 

 the orange gardens of Sirmio, and projected into the plains of 



Piedmont. By their mean if broken rock must have 



been transported into the lowlands ; but did they greatly modify 

 the peaks, deepen the valleys, or excavate the lake basins ? My 

 reply would be, "To no very material extent." I regard the 

 glacier as the file rather than as the chisel of nature. The Alpine 

 lakes appear to be more easily explained— as the Dead Sea can 

 only be explained — as the result of subsidence along zones roughly 

 parallel with the Alpine ranges, athwart the general directions of 

 valleys which already existed and had been in the main com- 

 pleted in pre-Glacial times. To produce these lake basins we 

 should require earth movements on no greater scale than have 

 taken place in our own country since the furthermost extension 

 of the ice-fields. This opinion as to the origin of the 1 I 



believe, generally held to be a heresy, but it is a heresy which 

 has been ingrained in me by some twenty years of study of the 

 physiography of the Alps. 



RECENT MORPHOLOGICAL SPECULATIONS 

 I. — On Alternation of Generations 



IT is more than sixty years since Chamisso pointed out that 

 in Salpa a solitary asexual individual produced a chain 

 of sexual individuals by budding, the viviparous eggs in these 

 becoming in turn the solitary form. This he made his type of 

 Alternation of Generations. 



Since his time the definition of this peculiar method of repro- 

 duction has been narrowed, and the alternation of a series of 

 individuals developed from an unfertilised egg, i.e. partheno- 

 genetically, and one or more generations of sexually produced 

 young is now called heterogamy ; the term metagenesis has been 

 invented for cases of alternation of sexual and gemmiparous 

 generations. 



Few instances can be cited where the study of a single genus 

 has brought out so many points of interest as in the case of the 

 pelagic Ascidian, Salpa. Two points in the history of this animal 

 still involved in controversy are the first phenomena of embryonic 

 development, and the mutual relationship of the two forms, the 

 solitary individual and the colony that swim united in a chain. 



As regards the former matter, the fate of the egg and the 

 origin of the nutritive structure known as the placenta present 

 great difficulties. 



While W. K. Brooks (Bull, of Museum of Comp. Zool., 

 Harvard University, iii.) believed that the egg undergoes a 

 regular segmentation resulting in the formation of a gastrula, the 

 cavity of which is divided by a transverse constriction into two 

 chambers, one becoming the "placenta," Todaro (At/i delta R. 

 Accad. dei Lined, Rome, 1875, 1880), on the other hand, stated 

 that the solitary Salpa is the result, not of the division of the 

 true ovum, but of the follicular cells inclosing it, and that 

 during development, which takes place in a special part of the 

 oviduct, the so-called uterus, a fold of the uterine wall forms a 

 decidua reflexa comparable to that of mammals. 



Salensky (Zool. Anzeiger, 1881 ; Mittheil. d. zool. Stat. z» 

 Neapel, Bd. iv.) accounts for some of these conflicting statements 

 by showing that great in nearly allied species, but 



he also declares that previous observations were often inaccurate. 

 He states that the fertilised ovum divides but slowly, and only 

 till the number of its segments reaches sixteen ; and that probably 

 it then entirely disappears, the tissues of the embryo being 

 formed from a varying number oifolluu'ar cells. In some cases, 

 as S. bicaudata, the so-called " decidua " is not represented. To 

 this most exceptional method of development he gives the name 

 of "follicular budding." 



Now the theory that Salpa is an instance of the alternation of 

 sexual and gemmiparous generations (i.e. of metagenesis), which 

 was put forward by Chamisso and supported by the researches 

 of Krohn, has been attacked by Brooks, who believes that the 

 solitary Salpa (which he calls the nurse) is hermaphrodite, and 

 gives rise by budding to a chain of males into each of which an 

 egg migrates from the nurse. This view of course supposes that 

 the solitary and chain forms belong to the same generation, they 

 being, in fact, respectively the sexually and asexually produced 

 Offspring of one and the same solitary hermaphrodite Salpa. 

 Todaro, on the other hand, states that, in the solitary adult, 

 certain of the follicular cells surrounding the ovum give rise to 

 no organs, but remain as cell-masses ; and that from these the 

 stolon is eventually developed. Hence the chain-Salpae are 

 developed parthenogenetically, and the nurse is an older sexless 

 form, serving to nourish the sexually complete chain. 



