913 



STORAX. 



STRATIFICATION. 



914 



known regarding the distribution of the fossils in the Oolitic Rocks. 

 Coniferous, Cycadeous, and Filicoid Plants; Lamelliferous Corals, 

 Conchifers, Gasteropoda, Cephalopods, Crustaceans, Insects, Ganoid 

 Fislies, Terrestrial and Aerial Saurians, Marsupial Mammalia; all 

 these occur together, and suggest to the naturalist a variety of infer- 

 ences aud speculations. Viewed in their most general relations, the 

 slaty beds of Stonesfield appear to be deposits produced in the sea 

 near the shore in shallow water, at points to which fresh-water cur- 

 rents might send, at intervals, some of the spoils of the land. The 

 Marine Conchifers are often found with valves united, and otherwise 

 in conditions which indicate residence on or near the spot where they 

 are buried ; but the broken state of the Land Plants, the scattered 

 elytra of Insects, the detached state of the teeth and bones of Fishes, 

 Saurians, and Mammalia, seem the effect of transport from some 

 distance. A great distance cannot well be supposed, for in that case 

 we must imagine the course of a great river, and look for its effects 

 over much wider areas than that of the Stonesfield Fossils. There 

 are several rather similar deposits, and perhaps of the same or nearly 

 the same geological date, in the Oolitic series of Northamptonshire 

 and Yorkshire, but they seem to be due to separate areas of littoral 

 agitation. The Fauna and Flora represented by these fossils is similar 

 to that which now exists in Australia, and has suggested the conclu- 

 sion that in Australia we have now a condition of the earth's surface 

 such as existed in Europe during the deposition of the Oolitic beds. 

 [OOLITE.] 



STORAX. [SrvRAX.] 



STORKS. [CICOKIA.] 



STRAMONIUM. [DATURA.] 



STRAND-WOLF. [HTO.ENINA.] 



STRAPWORT. [CORRIOIOLA.] 



STRATA. In Geology, both the separately deposited layers of 

 rock, and the rocks formed of these similar layers, accumulated 

 together, have received the name of Strata. Dr. William Smith uses 



In special and local descriptions of rocks, the several beds are com- 

 monly enough called Strata (Couches, French). As a general scheme 

 showing the rank frequently assigned to these and other terms, the 

 following view may be useful, the most comprehensive term being to 

 the left : 



Systems, Formations, Strata, Beds, Lamina?. 



The terms Series and Group are very conveniently employed to 

 collect under one head for purposes of reasoning, any of the lamina:, 

 beds, strata, formations, or systems (or parts of one formation and 

 parts of another), without any other limit than that imposed by the 

 principle of grouping. For instance, the Belemnitic Series of strata 

 includes the Lias Formation, Lower, Middle, and Upper Oolite For- 

 mations, and the Greensand and Chalk Formations; it includes two 

 systems of Strata : by the Trilobitic Series of strata we may under- 

 ntnnd the whole of the Palaeozoic Deposits, excepting perhaps the 

 Magnesian Limestone and the oldest of the Slaty Rocks. [3RATI- 

 KICATION; GEOLOOT.] 



STRATA, ALTERF.D. [ALTERED STRATA.] 



STRATIFICATION. Mineral masses, separately deposited, and 

 arranged into parallel layers under the influence of gravitation, com- 

 pose a large portion of the known rocky crust of the earth, and are 

 called Stratified Rocks; other masses, in which no such successive 

 deposition and tendency to be bounded by originally horizontal surfaces 

 is traceable, are locally prevalent, and receive the name of Uustratified 

 Rocks. They are generally supposed to be of igneous origin ; the 

 former are mostly known to be the fruit of sedimentary aggregat'o i 

 under water. To each class there are exceptions. Parts of certain 

 limestone rocks, fqrmed in water, as modern coral reefs, are really not 

 at all or very slightly stratified ; and certain melted rocks which have 

 spread in successive sheets like lava over ancient surfaces, or have 

 been forced by great lateral pressure between really stratified rocks, 

 often assume the stratiform aspect. Without now dwelling on these 

 and several other exceptional cases, it is our purpose to present a 

 general view of the present state of knowledge of the phenomena of 

 stratification, as exhibited in rocks which show clearly the fact of 

 their mineral particles having been separately subject, during the 

 aggregation of the mass, to the influence of gravitation, while partially 

 supported in media lighter than themselves, as water and air, and 

 generally influeuced by lateral movements, such as occur in a state of 

 nature in those almost universal fluids. 



1. Let us suppose a case of a shower of comminuted mineral matter 

 falling through a limited section of air on the ground. It will be 

 collected in a conical form, the slopes of the cone having reference to 

 the velocity of descent of the sandy particles, the mutual support they 

 yield one to another, and the form of the surface on which they fall. 

 Omitting these sources of variation, the slopes of the conical heap 

 will be generally within moderate limits of uniformity, aud the 

 inclination of these slopes constitutes what is called the ' angle of 

 rest.' A second shower of such sandy matters falling uniformly will 

 cover the cone with a parallel sheath, and thus conical strata may 

 result from such operations repeated. (Fig. 1.) The nearest analogy 

 to this type of stratification occurs iu a volcanic conu ; where however 



BAT. UIBT. DIV. VOL. IV. 



Fig. 1. 



Vertical section of strata formed by conical superposition (theoretical). 



the showers of ashes falling not uniformly, but in different quantities 

 in different directions, the result is a streamy or imperfectly con- 

 centric stratification, characteristic of the cause, and presenting on a 

 cross-section an appearance as in tig. 2. 



Fig. 2. 



Horizontal section of itrata formed by falling of ashes round a vertical axis 

 irregularly. 



2. If further we suppose a shower of ashes or sands to be much 

 affected while falling by horizontal currents of air, in this case the 

 supposed conical heaps of fiy. 1 will be drifted so as to show stratifi- 

 cation inclined or dipping from the windy quarter. (Fig. S.) Similar 

 effects might follow the drifting of sand which had fallen into heaps. 



Fig. 3. 



Laminated deposits of sand by the effect of wind. 



If the currents of air changed their direction at intervals, there 

 would arise complication of the strata oblique stratifications such 

 as are often seen in sandy rocks and sand-hills ; nnd these would be 

 more or less distinct as the interval between the winds had been 

 marked by vegetation, sediment, or any other cause of consolidation 

 of the surfaces. (Fig. 4.) 



Fig. 4. 



Oblique lamination in sand and gravel. 



3. On surfaces of loose sand once deposited, under whatever of the 

 influences stated, winds have the power of producing other effects : 

 winds eddying among the inequalities of partially grass-grown sand- 

 hills excavate in them circular, oval, or irregular pits, and make ridges 

 and crests of fantastic forms. (Fig. 5.) Winds also wear away by 



Fig. 5. 



Excavation of cavities in sandhills by wind. 



horizontal action the edges of these basins and crests, and make 

 appearances of level stratification, as water which changes level wears 

 its banks in parallel lines. Winds also by their peculiar action on 

 fluid or loose masses, which move with a different velocity from the 

 current of air, produce undulations on the surface of the sand lying 

 across the current, and much resembling the ' ripple or current mark ' 

 (which is a secondary phenomenon from the same cause) on the beds 

 of sand below agitated water. 



The falling velocity in air of the different sorts of mineral particles 

 which enter iuto the composition of rocks is not materially different, 

 even if the masses be considerably unequal in size ; but both in regard 



SN 



