32 



SCIENCE. 



[N. S. Vol. XV. No. 366. 



It is composed of three ankylosed vertebrae. 



It is interesting to find Dinosaurs in these 

 marine beds. The marine fossils are found 

 mixed with the bones. While digging out the 

 skeleton of Claosaurus nearly a dozen Nautali 

 were found among the bones. As a rule, when 

 bones are found a good part of the skeleton is 

 there or there is evidence that it has been. 

 Several skeletons had been found and the 

 bones removed for curiosities before I had 

 visited this region. The first skeleton I saw 

 was shown to me by a young man, Mr. Albert 

 Silberling, who lived on the ranch from which 

 the others were dug. I think that very few 

 fossil-hunters would have looked for Dinosaur 

 bones here. 



It seems that these deposits were made in a 

 shallow inland sea or an estuary which, at least 

 during a part of the time, was cut off from 

 the ocean, for in places there is considerable 

 gypsum. Perhaps we should hardly espect to 

 find such large marine mollusca in such a 

 place, but they evidently are not far from 

 where they died. There is no evidence of 

 strong tides, and if the shells had been washed 

 up by these or the winds they would be broken, 

 not complete as we find them. 



As a rule land animals are not very perfectly 

 preserved in marine deposits. In unearthing 

 these animals, therefore, the question is always 

 arising: "How did these bones get here?" 

 Did these Dinosaurs that have been so modi- 

 fied, evidently fitting them for life on land, 

 still retain their swimming habits, but occa- 

 sionally suffer shipwreck and their carcasses 

 sink to the bottom of the sea? By some in- 

 vasion of the sea were they forced to stay and 

 starve or 'swim for life' which jjroved in some 

 cases to be for death? I have seen no indica- 

 tions that they were killed by violence or their 

 carcasses destroyed by large carnivorous ani- 

 mals, though there has been a little disturbance 

 of the bones. Did they die on some mud flat 

 or did their carcasses float down some slug- 

 gish stream and get stranded in shallow water 

 or get 'water-logged' and sink in deeper 

 water? These are interesting questions, but 

 more thorough and careful investigation is 

 needed to decide the matter with any degree 

 of certainty. 



The University of Montana hopes before 

 very long to publish a bulletin describing these 

 beds and whatever is of interest in the collec- 

 tions obtained from them. 



Earl Douglass. 



Princeton, N. J. 



MAGMATIC DIFFEEENTIATION OF ROCKS. 



Since the time when the celebrated chemist 

 Bunsen first elaborated his theory on the na- 

 ture of rock magmas, the subject has been of 

 great importance to the geologist. If one were 

 asked to name three of the grander ideas which 

 mark the progress of geology during the cen- 

 tury just closed, this conception of magmatic 

 differentiation of rocks would certainly be one 

 of them. Of late years contributions to the sub- 

 ject have been numerous and important. Sev- 

 eral of the most recent are especially note- 

 worthy. 



In the reconsideration, by IT. S. Washing- 

 ton (Bulletin Geological Society of America^ 

 Volume XL), of the 'Igneous Complex of 

 Magnet Cove, Arkansas,' made exceptionally 

 interesting through the elaborate efforts of J. 

 Francis Williams, are recorded some observa- 

 tions on magmatic differentiation that are of 

 unusual significance at this time. Contrary to 

 previously expressed opinion, the several tsTpes 

 of deep-seated rocks represented in the com- 

 plex are regarded as integral parts of one great 

 mass and as contemporaneous in origin, and 

 therefore not due to successive intrusions. 

 Furthermore, the structure of the whole mass 

 is probably laccolithic in character. 



A remarkable feature connected with the 

 zonal distribution of the various rock-types is 

 the complete reversal of the order almost in- 

 variably found among large masses of cooled 

 magmas. Ordinarily the borders are basic and 

 the central parts more acidic. But in the 

 Magnet Cove mass the heavy constituents are 

 in the center and the lighter silica, alumina 

 and alkali components are on the edges. No- 

 table instances of similar character are re- 

 ported from Norway, Finland and Montana. 



The exceptional character of the Magnet 

 Cove mass appears to suggest unusual condi- 

 tions. While the general subject of the causes 

 of differentiation is not discussed at length, a 

 possible explanation for the Arkansas complex 



