514 



SCIENCE. 



[Vol. V., No. 125. 



or less widely than single photographs do under 

 similar conditions. The composites ought to 

 be almost wholly independent of fortuitous cir- 

 cumstances such as this ; and, although the sep- 

 arate negatives of the same individual might 

 exhibit considerable deviations from each oth- 

 er for one reason or another, yet such devia- 

 tions should have no cumulative effect in the 

 composite, but be in effect obliterated. If, 

 however, there is, as there well may be, some 

 personal peculiarity in the adjustments of a 

 photographer, his composite will necessarily 

 bear the impress of this mannerism, and fur- 

 nish a kind of personal error, which can per- 

 haps be only eliminated by making a composite 

 from a number of composites of the same 

 group, each taken by a different person. 



LETTERS TO THE EDITOR. 

 A modern type of plant in the cretaceous. 



The genus Braseniee, or Hydropeltis, is represented 

 in eastern North America by a single species, 13. pel- 

 tata, Pursh (Hydropeltis purpurea, Michaux), which, 

 according to Gray, is also a native of Puget Sound, 

 Japan, Australia, and India. A form so widely dis- 

 tributed may be expected to have been early intro- 

 duced, so that we need not be surprised to find it 

 occurring along with tbe earlier forms of exogenous 

 life in the cretaceous of our north-west. 



The specimens to which this note refers were ob- 

 tained in the beds of the Belly-Kiver series of the 



BRASENieB- ANTIQUA, UPPER CRETACEOUS, SOUTH SASKATCHE- 

 WAN RIVER. LEAF NAT. SIZE. a,b, DIAGRAMS OF VENATION, 

 SLIGHTLY ENLARGED. 



Canadian survey, near Medicine Hat. These beds 

 are upper cretaceous, and hold fossils, some of which 

 resemble those of tbe Laramie group, others those of 

 tbe Pierre group. They contain workable beds of lig- 

 nitic coal; and the specimens in question were found 

 in nodular clay ironstone, associated with one of the 

 coal-beds worked in the ' Lawson mine.' 



A specimen of this interesting fossil, obtained, I 

 believe, from Mr. Lawson, tbe manager of the mine, 

 was kindly given to me last year by Mr. J. R. Byron, 

 one of the members of tbe British association; and 

 additional specimens, some of them very perfect, were 

 afterwards collected by Mr. T. C. Weston of the geo- 

 logical survey. They resemble very closely the leaves 



of the modern species, differing only in their generally 

 smaller size and somewhat less elliptical form, and 

 slightly in the venation, the primary veins being more 

 numerous, or about eighteen in number, while four- 

 teen is a common number in the modern species. 

 These differences may indicate merely a varietal 

 form; but I have thought it best to designate the 

 species or variety by the name B. antiqua. Associ- 

 ated with these leaves, in the same bed, are some other 

 aquatics, notably Pistia corrugata (Lesqx.) and Lem- 

 na scutata (Dn), both species of the Laramie; and 

 Platanus nobilis of Newberry (Aralia notata of Les- 

 quereux), which, though apparently regarded in the 

 United States as miocene, is certainly in Canada 

 characteristically Laramie. There is also a new spe- 

 cies of Populus — P. latidentata (Dn) — closely allied 

 to the modern P. grandidentata, and an Acer (A. sas- 

 katchewense), whose leaves resemble small or imma- 

 ture leaves of A. dasycarpum. A species of Sequoia 

 also occurs, probably S. Reichenbachii. Though all 

 these plants have a very modern aspect, they are un- 

 questionably cretaceous; and I have myself assisted 

 at the disinterment of a dinosaur of the genus Di- 

 clonius from beds overlying those in which the leaves 

 occur. These facts furnish another instance of that 

 modern aspect of the upper cretaceous flora on which 

 I have elsewhere insisted, and which has been a fer- 

 tile source of error with reference to the age of beds 

 of this formation in the west. It is interesting to 

 note that beds of this age in western Canada contain 

 the modern Onoclea sensibilis of America, along with 

 Davallia tenuifolia, also modern, but now Asiatic. 



J. \Vm. Dawson. 



Lateral movements of the earth's crust. 



While observations are being made for the pur- 

 pose of investigating ' variations of latitude,' is it 

 not desirable that the U. S. coast and geodetic sur- 

 vey should make simultaneous observations with a 

 view to discover, if possible, whether or not places 

 along our coasts are suffering changes of latitude or 

 longitude, or both, due to lateral movements of the 

 earth's crust ? 



If it is true that during geological history large 

 lateral movements of the earth's crust have taken 

 place, and if such changes are still going on, it 

 would seem inevitable, that, in regions where lat- 

 eral displacements are taking place, landmarks should 

 suffer a change of latitude or longitude, or of both, 

 according to the direction of yielding to lateral press- 

 ure, and that places located upon regions suffering 

 compression or folding should be moved, to some 

 extent, bodily toward places in adjoining regions, 

 toward which the movements take place, but which 

 are not themselves undergoing displacements. 



Since vertical movements of the earth's crust are 

 taking place at measurable rates, and since, in the 

 past, lateral movements appear to have exceeded the 

 vertical, it might be expected, that lateral move- 

 ments are now taking place at measurable rates. 

 Of course, if the superficial strata are not involved 

 in these movements, the deeper strata only yielding, 

 surface landmarks could not reveal the movement; 

 but in this case, and in case folds of the superficial 

 strata along our coasts are in process of evolution, 

 it would seem that such changes might be discovered 

 by sinking deep vertical shafts at intervals along 

 lines normal to the coast. These carefully surveyed 

 at intervals during one or two centuries, it would 

 seem, should show a measurable warping or tilting 

 if such movements are going on. F. H. King. 



River Falls, Wis. 



