306 



SCIENCE. 



[Vol. XXII. No. 565 



a great measvire dispose of the origin of the middle great 

 division. 



Now whether the great series of deposits immediately 

 overlying the marine beds — the Yegua clays — have been 

 altogether derived from the erosion and consequent de- 

 struction of the marine beds is not very clear. That a 

 portion of the materials composing these clays was so 

 derived there can be no doubt. The line of contact be- 

 tween the two is very irregular in more than one place, 

 showing long troughs or valleys of erosion in the older 

 beds, and now filled up by the clays and sands of the 

 newer. At other places this outline shows the existence 

 of comparatively bold head-lauda, from which no doubt 

 the waters of Yegua time abstracted a considerable quan- 

 tity of material. The presence of extensive deposits of 

 lignites in these beds would appear to indicate another 

 source of material having a swamp or lagoon origin, and 

 some of it may have been obtained from the rivers travers- 

 ing the region. Some of the materials employed in the 

 formation of these beds may also have been derived from 

 the sea water occupying the area during the period of 

 dei^osition. 



The last division, or more properly speaking, the sec- 

 ond division — the lignitic beds — presents somewhat dif- 

 ferent features from any of the others. So far as it con- 

 tains immense deposits of lignite and small beds of sand 

 carrying crystals of selenite, it resembles the Yegua clays, 

 but with that its resemblance ceases. The beds belong- 

 ing to this division overlie the basal deposits, which in 

 many places they overlap) so completelj' as to obscure 

 them altogether, and in others lie in direct contact with 

 the Cretaceous deposits. Throughout the whole of the 

 immense thickness and extent of these beds, with the ex- 

 ception of a few fragmentary plant remains, some of them 

 belonging to the sabal family, not a single fossil is known 

 from this division. Evidently the conditions were not 

 favorable to animal life. 



These beds apparently represent a period when the 

 whole coast was made up of swamps, lagoons and bayous, 

 very similar to some portions of the gulf coast of the 

 present day, or what may be seen in the broad stretches 

 of overflow or "bottom" land found along almost every 

 one of our rivers. A rank vegetation grew on the marshy 

 portions, and the rivers of the time having no fixed chan- 

 nels, distributed their waters throughout the lagoons and 

 baj'ous and into them, and over the low islands carried 

 their burdens of debris during periods of flood. With 

 this debris came soft clay, sand, branches, limbs and 

 trunks of large trees, all of which went to swell the 

 accumulations already gathering and aid in the formation 

 or the lignites and their associated beds of clay and sand. 

 In the meantime the coast was slowly sinking and the 

 encroaching water eating away the basal clays and 

 the Cretaceous deposits within reach. 



The lithological structure of these deposits accord with 

 these conditions. Everj'where the deposits are irregular 

 in deposition, variable in texture, changing from fine- 

 grained, dense, muddy, to coarse-grained, sandy material 

 within short distances. Many of the beds contain great 

 quantities of iron jjyrites, a common characteristic of the 

 Cretaceous greensand marls. In composition these lig- 

 nitic beds closely resemble these marls. 



Sulphuric acid. 

 Carbonic acid, 

 Water and loss, 



4.26 



1.06 



2.85 



3-53 



Silica, 



Alumina, 



Iron, - 



Lime, 



Magnesia, 



Potash, 



Soda, 



IV. 

 . of 38 analy- 

 of lignitic 

 clays. 

 69.83 

 16.93 

 3-66 

 0.77 

 0.35 

 1-35 

 3.42 



V. 



Cretaceous 



greensand 



marls- 



60. 82 



16.05 



5-25 



3-66 



1-75 

 2.94 



100.79 99-91 



From this, then, it would appear that while the greater 

 portions of these clays and sands are derived from Creta- 

 ceous materials, these have been mixed with a small quan- 

 tity of ingredients belonging to some of the older forma- 

 tions through which the larger rivers ran; but the proj)or- 

 tions of these older materials were so small as not to 

 visibly afl^ect the deposits as a whole. 



Mention has been made of the syenitic rocks of Arkan- 

 sas and the basaltic outbreaks extending through the 

 Texas Cretaceous area as forming the source of some of 

 the materials found in the clays. These I do not think 

 can have contributed any of the materials required. No 

 very decided evidence of the age of these rocks has been 

 given, but the general opinion as stated by Branner and 

 Williams appears to be that the age of the Arkansas rocks 

 is ether late Cretaceous or early Tertiary, and certainly 

 not newer than this time. According to Hill, Pilot Knob 

 belongs to the upper Cretaceous and the latter half of 

 Austin Chalk sub-epoch. If these ages are accepted, 

 then certainly the rocks in question had nothing to do 

 with the formation of the Texas Tertiary clays. 



KARYOKINESIS IN EMBRYOS OF THE DOM- 

 ESTIC CAT.— PRELIMINARY NOTICE. 



I;Y rR.A.NK S. ABY, HISTOLOGICAL LABORATORY, STATE UNI- 

 VERSITY OF .IOWA. 



In all sections of various embryo kittens that have 

 been examined by the writer, np to those of embryos 

 seventeen millimetres in length, karyokinetic figures 

 are by no means an occasional or a rare occurrence, but 

 are to be found in many situations. 



In the preparation of these sections, no special cyto- 

 logical methods were employed, as the subject of in- 

 vestigation was the development of the central nervous 

 system of the cat. The embryos were hardened in 

 increasing strengths of alcohol, with no precautions 

 whatever with regard to fixation. After remaining in 

 95 per cent alcohol for a number of months the embryos 

 were imbedded in celloidin and sectioned. The sections 

 were then stained in Grenacher's haematoxylin and 

 mounted in Canada balsam. 



The resting nuclei are spheroidal occasionally, but 

 the more usual form is that of an elongated oval. Occa- 

 sionally very peculiar, irregular nuclei are found, and 

 one was seen whose length was three times its width, 

 without the aggregation of chromatin to be described 

 later, but with a clearly marked reticulum and nuclear 

 membrane. Usuallv the nuclear membrane is not 

 shrivelled or wrinkled in hardening, but is plump and' 

 distinct, clear cut on its outer line, and in almost all 

 cases has taken a deep stain. 



The chromatin in these resting nuclei is disposed in a 

 reticulum that strongly reminds one of the bridles seen 

 in plant cells. This reticulum is clearly continuous 

 with the nuclear membrane, as may be seen in very 

 numerous instances, the point of union of a strand and 

 the nuclear membrane presenting a well-defined en- 

 largement of the strand. In some nuclei which happen 

 to lie in the proper position several of these points of 

 union in a single nucleus appear in the same plane, 

 giving the nuclear membrane the appearance of being 

 toothed. 



