6o4 



NA TURE 



[Oct. 27, 1887 



our mountains have been largely determined by their geological 

 structure, and by faults, contortions, and subsidences in the strata 

 of which they are composed. 



I cannot argue this question here. Suffice it to say that the 

 "Great Gutter Theory," as I venture to call it, does not, in my 

 opinion, explain our hills or our glens. There has been, no 

 doubt, enormous denudation. But " in the main " the forms 

 express structure, and the effects of subterranean force. 



Mr. Green refers to the "graphic illustrations" of Mr. 

 Geikie's book. But unfortunately those illustrations are some- 

 times very incorrect. For example, the general view given of the 

 south-western termination of the Highland ranges, as seen from 

 above Gourock on the Clyde, is a view as defective and incorrect 

 as it is possible for a geological landscape to be. I know that 

 range of hills well, and have seen it since my childhood in every 

 variety of light and shadow. I have also drawn it frequently, and 

 know almost every line of it by heart. It presents a section across 

 a great anticlinal, as was first pointed out to me by Murchison ; 

 and it is full of surface markings which reveal its structure. Not 

 one line of these is given in Mr. Geikie's drawing. If he had 

 been sketching a set of mole-hills he could not have made 

 them more featureless — more utterly devoid of their distinctive 

 forms. 



Let us have facts before theories. Let us have our hills so 

 drawn as to express the lines of structure as they are seen in 

 Nature, and in their relation to outline. But very often the eye 

 sees nothing except what the brain behind it has preconceived ; 

 and a geologist who draws a mountain with a theory of guttering 

 in his head, is pretty sure to make a mess of it. 



There is really nothing in the argument about an average level 

 along the tops, as any sure indication of an original "table- 

 land," with all its hollows due to guttering. All sedimentary 

 materials having an average composition, when subjected to 

 strains, pressures, or fractures, would, and must, exhibit average 

 resulting forms. This general fact is equally consistent with 

 more than one explanation. 



I believe Mr. Geikie has modified his former views as to the 

 action of ice. A closer inspection of the Highlands will, I am 

 convinced, modify greatly in other ways his teaching as to the 

 small share which structure, and subterranean force, have had in 

 determining the physical geography of the country. 



October 15. Argyll. 



In your last issue Prof. A. H. Green, reviewing Dr. A. 

 Geikie's "The Scenery of Scotland viewed in Connexion with its 

 Physical Geology," described the alleged resemblance between 

 the Durness fossils and certain North American types as "an 

 announcement of the greatest interest." The fact is certainly of 

 the "greatest interest," but the " announcement " was made 

 nearly thirty years ago by the late J. W. Salter in the Quarterly 

 /(?M;'«a/ of the Geological Society, 1858, p. 381. Mr. Salter refers 

 to the fauna as "this truly North American assemblage," and 

 compares the species one by one with Prof. Hall's types. 



Ch. Callaway. 



Wellington, Shropshire, October 16. 



[We have referred these letters to Mr. Green, who has sent 

 us the following reply. — Ed.] 



It is well known that the Duke of Argyll has long been a 

 strenuous and consistent opponent of the views as to the origin 

 of the surface features of the earth which are accepted by the 

 majority of geologi-ts. Indeed, if I had been disposed to be 

 personal, I do not think that I could have quoted a more perti- 

 nent illustration than his Grace of a fact in the history of opinion 

 to which I drew attention in the opening part of my review of 

 the " Scenery of Scotland." He hears not Moses and the 

 prophets, and I fear he will not be persuaded by the pleadings 

 of one of their humbler followers ; but if he will let me have my 

 small say, I will first point out that his objection to the expres- 

 sion " surface features " seems to me to savour a little of quib- 

 bling. It is a general rule of criticism to interpret any ambiguous 

 words by the context. The whole tenor of my article shows 

 that I did not use the words in the first of the two meanings 

 which the Duke says they may bear. Again, I an quite pre- 

 pared to admit that geological structure has had a large share in 

 determining the form of the ground ; and I cannot find that 

 either Dr. Geikie, or any other upholder of the Gutter Theory 

 (I thank thee, Duke, for teaching me that word : no happier 

 designation could be found), denies that subterranean force has 



played an important part in determining the physical geology of 

 a country. Rather the contrary, for hear Dr. Geikie himself 

 He avows himself wishful that his reader should " recognize 

 that a belief in the paramount efficacy of superficial denudation 

 in the origin of the features of the land is compatible with the 

 fullest admission of the existence and potency of subterranean 

 disturbance. Inability to make this recognition," he says, "has 

 led to absurd misconceptions and misrepresentations of the views 

 of those who hold that the topography of the land is essentially 

 the result of a process of sculpture" ("Scenery of Scotland," 

 pp. 95, 96). 



I will leave Dr. Geikie to take care of himself and defend the 

 drawing the accuracy of which is impugned by his critic. I do 

 not know the special landscape of Fig. 19, but I have enjoyed 

 a few panoramic views of Highland scenery, and I can honestly 

 say thus much : I have everywhere recognized those surface 

 fnarkings (may I again congratulate his Grace on the happiness 

 of this phrase ?) which indicate the geological structure of the 

 ground beneath, but I have in every case been still more struck 

 by that general flat-toppedness on which special stress is laid by 

 Dr. Geikie. The comparatively slight prominence given to these 

 surface markings in Fig. 19 will be easily understood if w 

 bear in mind the one pomt which that cut was intended to 

 illustrate. 



I may add that I am extremely sorry if any words of mine 

 seem to imply that I grudge my old friend Salter the credit due 

 to him with regard to the Durness fossils. The expression I 

 have used could be made to bear this meaning, and I am much 

 obliged to Dr. Callaway for giving me an opportunity of dis- 

 avowing any such intention. A. H. Green. 



Leeds, October 20. 



A Hydroid Parasitic on a Fish. 



During my studies the past summer at the Newport Marine 

 Laboratory I captured a single specimen of an osseous fish, 

 Seriola zonata, Cuv., which exhibits a most interesting example 

 of parasitism or possibly commensalism. Upon the outer wall 

 of its body an extraordinary hydroid was found to have attached 

 itself. As this mode of life is unique for a hydroid, it is thought 

 that a mention of it, and a statement of the peculiar modifica- 

 tions which the hydroid has suffered, may be not without 

 interest to others besides special students of the jelly-fishes. The 

 hydroid is new to science, and on that account the name 

 Hydrichthys is suggested to designate it. The hydroid will 

 later be described and figured under the name Hydrichthys 

 mil-US, gen. et sp. nov. 



The colony of Hydrichthys is found on the side of the body 

 and near to the anal fin of the fish, Seriola. It forms a reddish 

 cluster or patch of bodies, and was at first mistaken for a fun- 

 goid growth. When it was examined by means of a microscope 

 its animal nature was easily seen and its hydroid affinities clearly 

 made out. The fish was kept alive in an aquarium and 

 medusae raised from the attached hydroid. The hydroid colony 

 is composed of two sets of individuals. These two kinds of 

 individuals arise from a flat plate formed of branching tubes, by 

 which the colony is attached to the body of the fish. The two 

 kinds of individuals noticed in the cluster are the sexual bodies | 

 (gonosomes), and the "filiform bodies" (structures of unknown! 

 function). i 



The sexual bodies have the form of grape-like clusters of buds ; 

 mounted on small contractile peduncles, which branch from aj 

 central axis or stalk. The filiform bodies are simple, elongated, ; 

 flask-shaped structures, destitute of appendages, with a central; 

 cavity and terminal orifice. Neither of these two kinds ol. 

 individuals have tentacles around or near a mouth opening, noi 

 any structures which can be compared with these bodies, which 

 are almost universal among fixed hydroids, _ 



The first kind of individuals are the gonosomes or sexu 

 bodies. They arise from the flat basal plate of branching tuM 

 by which the union of the colony with the outer wall of the J 

 is effected. Each hydroid gonosome consists of a main stl 

 with lateral branches. At the end of each lateral branch theK 

 is a crowded cluster of small buds, which are immature jelly- 

 fishes in all stages of growth. Each gonosome resembles^ 

 bunch of reddish and orange-coloured grapes. 



The filiform bodies are simpler in structure than the sex 

 clusters or gonosomes. They are destitute of tentacles and j 

 flask-like, with a cavity and terminal orifice. They are 

 sensitive, and move about with freedom, never, however, be 



