who has seen the locality fail to appreciate the fitness of the structure for the singular combination of difficulties which are presented.

Your Engineer, Mr. Alexander Ross, has personally examined the Niagara Bridge since its opening, with the view of instituting, as far as is practicable, a comparison between that kind of structure and the one proposed for the Victoria Bridge; and as he has since communicated to me by letter the general conclusions at which he has arrived, I think I cannot do better than convey them to you in his own words, which are subjoined below:

"I find from various sources that considerable pains have been taken to produce an impression in England in favour of a Suspension Bridge in place of that we are engaged in constructing across the St. Lawrence at this place. This idea, no doubt, has arisen from the success of the Niagara Suspension Bridge, lately finished by Mr. Roebling, and now in use by the Great Western Railway Compa ny, as the connecting links between their lines on each side the St. Lawrence, about two miles below the great 'Falls,' of the situation and particulars of which you will no doubt have some recollection. I visited the spot lately, and found Mr. Roebling there, who gave me every facility I could desire for my objects. Of his last report on the completion of the work he also gave me a copy, which you will receive with this: I have marked the points which contain the substance of his statement. I also enclose an engraved sketch of the structure. Mr. Roebling has succeeded in accomplishing all he had undertaken, viz.: safely to pass over railway trains at a speed not exceeding five miles an hour; this speed, however, is not practiced, -the time occupied in passing over 800 feet is three minutes, which is equal to three miles an hour. The deflection is found to vary from to 9 inches, depending on the extent of the load, and the largest load yet passed over is 326 tons of 2000 lbs. each, which caused a depression of ten inches. A precaution has been taken to diminish the span from 800 to 700 feet, by building up, underneath the platform at each end, about forty feet in length intervening between the towers and the face of the precipice upon which they stand; and struts have also been added, extending ten feet further. The points involved in the consideration of this subject are, first, sufficiency, and second, cost. These are, in this particular case, soon disposed of. First, we have a structure which we dare not use at a higher speed than three miles an hour; in crossing the St. Lawrence at Montreal we should thus occupy three-quarters of an hour; and allowing reasonable time for trains clearing and getting well out of each other's way, I consider that twenty trains in the twenty-four hours is the utmost we could accomplish. When our communication is completed across the St. Lawrence, there will be lines (now existing, having their termini on the south shore) which, with our own line, will require four or five times this accommodation. This is no exaggeration. Over the bridge in question, although opened only a few weeks, and the roads yet incomplete on either side, there are between thirty and forty trains pass daily. The mixed application of timber and iron in connection with wire, renders it impossible to put up so large a work to answer the purposes required at Montreal; we must, therefore, construct it entirely of iron, omitting all perishable materials; and we are thus brought to consider the question of cost. In doing which, as regards the Victoria Bridge, I find that, dividing it under three heads, it stands as follows:

First, the approaches and abutments, which together extend to 3000 feet in length, amount in the estimate to.

..£200,000

Second, the masonry, forming the piers which occupy the intervening space of 7000 feet between the abutments, including all dams and appliances for their erection .....

..£800,000

Third, the wrought iron tubular superstructure, 7000 feet in length, which

amounts to.

.£400,000

(About £57 per lineal foot.)

Making a total of ....

£1,400,000

"By substituting a Suspension Bridge the case would stand thus: -The approaches and abutments extending to 3,000 feet in length being common to both, more especially as these are now in an advanced state, may be s.ated as above at £200,000.

"The masonry of the Victoria bridge piers ranges from 40 to 72 feet in height averaging 56 feet and these are 24 in number, the number required for a suspension bridge admitting of spans of about 700 feet, would be 10, and these would extend to an average height of 125 feet.-These 10 piers, with the proportions due to their height and stability, would contain as much (probably more) masonry as is contained in the 24 piers designed for the Victoria bridge, and the only item of saving, which would arise between these, would be the lesser number of dams that would be required for the suspension piers; but this I beg to say, is more than doubly balanced by the excess in masonry, and the additional cost entailed in the construction, at so greatly increased a height. Next as to the superstructure, which in the Victoria bricge costs £57 per lineal foot,-Mr. Roebling in his report states the cost of his bridge to have been $400,000 which is equal to £80,000 sterling. Estimating his towers and anchor masonry at £20,000 which I believe is more than their due: We have 60,000 left for the superstructure, which for a length of 800 feet is equal to £75 per lineal foot, giving an excess of £18 per foot over the tubes of which we have 7,000 feet in length.-By this data, we show an excess of nearly 10 per cent. in the suspension as compared with the tubular principle, for the particular locality with which we have to deal, besides having a structure perishable in itself, on account of the nature of the materials; and to construct them entirely of iron, would involve an increase in the cost which no circumstance connected with our local or any other consideration at Montreal, would justify. We attain our ends by a much more economical structure, and what is of still greater consequence a more permanent one; and as Mr. Roebling says, no suspension bridge is safe without the appliances of stays from below, no stays of the kind referred to could be used in the Victoria Bridge,—both on account of the navigation and the ice, either of which, coming in contact with them, would instantly destroy them. No security would be left against the storms and hurricanes so frequently occurring in this part of the world.

"No one, however, capable of forming a judgment upon the subject, will doubt for one moment the propriety of adopting the suspended mode of structure for the particular place and object it is designed to serve at Niagara. A gorge 800 feet in width and 240 in depth, with a foaming cataract racing at a speed from 20 to 30 miles an hour, underneath, points out at once that the design is most eligi ble; and Mr. Roebling has succeeded in perfecting a work capable of passing over ten or twelve trains an hour, if it should be required to do so. The end is attained by means the most applicable to the circumstances; these means, however, are only applicable where they can be used with economy, as in this instance.'

"My own sentiments are so fully conveyed in the above extract from Mr. Ross'

letter, that I can add no further remark upon the subject, except perhaps that there appears to be a discrepancy in that part which relates to cost.

In dividing the £80,000 into items, Mr. Ross has deducted £20,000 for masonry, and left the residue, £60,000, for the 800 feet of roadway. Now it appears evident that this amount should include the cost of the "land chains;" and assuming their value at about £15,000, there would be only £45,000 left for the 800 feet of roadway, thus reducing the cost per lineal foot to about that of the tube. But in the application of a suspension bridge for the St. Lawrence the item £15,000 for "land chains" would of course have to be added to the cost of the 7,000 feet of roadway, which would swell the amount per foot to a little over that of the tubes."

*

"I entirely concur in what Mr. Ross says respecting the propriety of applying the suspension principle to the passage across the Niagara gorge; no system of bridge building yet devised could cope with the large span of 800 feet which was then absolutely called for, irrespective of the other difficulties attended to. "Where such spans are demanded, no design of beam with which I am acquainted would be at all feasible. The tube, trellis, and triangular systems are impracticable in a commercial sense and even as a practical engineering question the difficulties involved are all but insurmountable.

"Over the St. Lawrence we are fortunately not compelled to adopt very large spans, none so large in fact as have been already accomplished by the simple 'Girder' system. It is under these circumstances that the suspension principle fails, in my opinion, to possess any decided advantage in point of expense, whilst it is certainly much inferior as regards stability for railway purposes. The flexure of the Niagara Bridge, though really small, is sufficiently indicative of such a movement amongst the parts of the platform as cannot fail to augment where wood is employed, before a long time elapses.

"I beg that this observation may not be considered as being made in the tone of disparagement; on the contrary, no one appreciates more than I do the skill and science displayed by Mr. Roebling in overcoming the striking enginnering difficulties by which he was surrounded; I only refer to the question of flexure in the platform as an unavoidable defect in the suspension principle, which from the comparatively small spans that are available in the Victoria Bridge may be entirely removed out of consideration."

It may be questioned whether the circumstances of the railway traffic demanded the immediate construction of a railway bridge at Montreal of any description, but it is not our purpose to discuss that question here. We feel confident, however, that the exceedingly expensive structure now being erected cannot be justified while a much less costly one was within reach. While fully admitting the force of all Mr. Stephenson's arguments in favour of the tubular principle, as in comparison with other principles of construction in iron, and as compared with the suspension principle for the particular case in question, we regret that he did not more fully consider the fitness of a wooden superstructure, which we feel con

K*

vinced would have met every exigency of the case; and under careful supervision and due watchfulness against fire, if properly constructed, would have been free from all the objections as to flexure, and consequent decay, which Mr. Stephenson urges against wood as applied to suspension bridges, and would have endured until a more complete development of the railway traffic might warrant the enormous expenditure now being incurred;-thus saving a present outlay of upwards of £300,000.

A. B.

SCIENTIFIC AND LITERARY NOTES.

GEOLOGY AND MINERALOGY.

NEW CRUSTACEANS FROM THE SILURIAN ROCKS OF SCOTLAND.

The February Number of the Quarterly Journal of the Geological Society of London, contains a series of papers of much interest on several new forms of Crustacea from the Parish of Lesmahago in Lanarkshire. These were discovered by Mr. Robert Slimon. The beds in which they occur have been examined by Sir Roderick Murchison and Professor Ramsay, who consider them to belong to the top band of the Upper Silurians-the equivalents of the "Tilestones or Upper Ludlow series, previously unrecognised in that part of the country. The fossils discovered by Mr. Slimon have many apparent affinities with Eurypterus or Pterygotus. As shewn by Mr. Salter, however, they constitute no less than five distinct species of a new genus, named by him, Himantopterus, from the peculiar thong-like aspect of the swimming feet. The eyes are apparently situated on the extreme lateral margin of the anterior portion of the head-shield : a character serving to distinguish these new forms very readily from Eurypteri, which, otherwise, in general appearance they much resemble. Of the chelate antennæ, however, there appears to have been only a single pair. The largest of the discovered species is considered to have been at least three feet in length. Professor Huxley has appended some very able remarks to Mr. Salter's descriptions, in which he points out many striking relations between this new genus Himantopterus, and a particular section of the Stomapods on the one hand, and certain larval forms of Macroura (the “zoæa” of a few years' back) on the other. Amongst the Lanarkshire specimens also, discovered by Mr. Slimon, were some very complete forms of the genus Ceratiocaris of M‘Coy, previously very imperfectly known.

ASAPHUS CANADENSIS.

Specimens of Asaphus platycephalus-the Isotelus gigas of many authors, are well known to abound amongst the trilobites from the Utica Schist of Whitby, Port Hope, &c., in Canada West. After Triarthrus Beckii, the species in question is perhaps the most abundant fossil of these localities. The principal feature in Asaphus platy

cephalus, at least in adult individuals, is the comparatively undivided character of the caudal shield. In the Whitby schists, however, trilobites occur, over seven or eight inches in length (if not longer,) with the caudal extremity not only distinctly trilobed, but also marked with numerous and distinct pleuræ extending almost to the edge of the striated limb; whilst at the same time, they agree in all other respects with A. platycephalus. In the union of the facial suture above the glabella, for example, the two are alike; and in the peculiar character of the body-segments and pleura, not the slightest difference is perceptible. As no figure of this trilobite is given in Hall's Paleontology, and as the form appears to differ from the figured European species, we propose to confer upon it provisionally the name of Asaphus Canadensis. If it be really new, it may be placed as the type of a particular subdivision of the Asaphidæ, in accordance with the following scheme :

Asaphide with facial sutures united:

§1. Pygidium, undivided :-Type, A. platycephalus.

§2. Pygidium with grooved axis:-Type, A. expan us.

§3. Pygidium with grooved axis and pleuræ :-Type, A. Canadensis. A drawing of this latter species will be given in the second part of our Paper on the Trilobites

MINERALOGICAL NOTICES.

Dufrenoysite-Ch. Heusser has communicated to Poggendorff's Annalen (1856, No. 1.) some additional information on the crystallization of Dufrenoysite [2 (PbS) + As2 S3] from the dolomite of the Binnenthal He confirms the Monometric character of the mineral; but, in addition to the forms hitherto discovered, viz:-the rhombic dodecahedron, and the leucitoid 2-2, he announces the cube, the octahedron, a second leucitoid 6-6, and a trisoctahedron 2. Hardness, $4.5

Binnite:-Heusser has also subjected to a detailed examination, the steel-grey metallic sulphide which often accompanies the Dufrenoysite at the above locality. This mineral has been known in Switzerland for some time under the name of Binnite. It occurs in very small and longitudinally striated prisms of extreme brittleness. Streak, dark-red, much darker than that of Dufrenoysite; specific gravity (according to an earlier determination of Von Waltershausen on specimens taken by him for Dufrenoysite) 4.477. These latter specimens, according to Uhrlaub, contained sulphur, arsenic and copper, with a mere trace of lead. The system of crystallization of Heusser's specimens, was apparently Trimetric, but the prism-angle could not be obtained, owing to the stria on the faces. The measured angles, those of a series of domes, but whether macrodomes or brachydomes not determinable, did not accord with the measurements obtained by Von Waltershausen. An examination of further specimens is consequently desirable.

Hyalophane:-The dolomite of this same locality furnished to Von Waltershausen another mineral, which he described as new, under the name of Hyalophane. It was thought to contain: SiO3, Al2O3, CaO, MgO, NaO, BaO, SO3, and HO. Heusser has shewn, however, that it is simply an adularia variety of Orthoclase, containing accidental particles of Iron pyrites, and interpenetrated by Dolomite and Heavy Spar. Seven distinct crystals carefully freed from these impurities, and tested respectively by the blowpipe, did not yield the slightest trace of sulphur.

Rhodonite: Crystals of the Silicate of Manganese, or Rhodonite, are, it is wellknown, of rare occurrence. From those hitherto met with, and from the cleavage planes of massive specimens, the crystallization of the mineral has been long considered identical with that of Augite or Pyroxene: a supposition apparently con