82 



HARD WICKE 'S SCIENCE . G OSSIP. 



quantities are retained in them temporarily, we are 

 not prepared to state ; but it does not seem likely 

 that the rates of absorption and evaporation have 

 varied much. A certain portion of the water, how- 

 ever, remains in the rocks for prolonged geological 

 periods, and it is believed the amount is constantly 

 increasing. It is not known what the amount may 

 be, but there seems to be no reason to suppose that 

 it has affected the volume of the ocean to any large 

 extent. The conclusion at which we arrive is that at 

 every geological period there has probably been water 

 somewhere on the earth's surface, having a mean depth 

 of over 9,000 feet. It has been suggested that comets' 

 tails may have condensed on the earth, and, as a conse- 

 quence, given rise to floods ; but such speculations may 

 be dismissed as purely imaginative. The attractive in- 

 fluence of the land draws the ocean above the level it 

 would otherwise have, and thus causes the water to 

 encroach upon the land ; but such elevation of the 

 water is a local phenomenon only, the mean level of 

 the ocean being in no way affected. 



The existence and, to a large extent, the conditions 

 of the present sea are indicated by direct evidence ; . 

 but the position, depth, and conditions of the seas of 

 former periods can only be ascertained by indirect 

 means ; and mainly from the fossil remains found in 

 strata. The occurrence of a species belonging to a 

 group of organisms which, so far as known, is exclu- 

 sively marine, is a fair proof of the co-existence of 

 marine conditions, provided, of course, such remains 

 have not been introduced by accident or by derivation 

 from older marine beds. In most cases collateral 

 evidence sufficiently indicates whether the stratum is 

 or is not marine. The distribution of marine or- 

 ganisms is dependent upon circumstances, so that a 

 study of these in the case of living species enables us 

 to infer, more or less correctly, some of the condi- 

 tions of the sea in which they lived ; and amongst 

 others that of the contour or depth. The matter is, 

 however, somewhat complicated, for it would seem 

 that depth alone has little influence on the distribu- 

 tion of animals and plants, and that the influencing 

 conditions are temperature, light, food, currents, &c. 

 The evidence then which fossils afford as to depth is 

 probably wholly circumstantial. In the present seas 

 the greater depths are associated with a low tem- 

 perature, slow currents or movements of water, sedi- 

 ments of extreme fineness, and absence of solar lumi- 

 nous rays ; the probabilities are that such has always 

 been the case in the older oceans ; but the only con- 

 stant condition associated with great depth is absence 

 of the sun's light. In closed seas the temperature 

 may be high at great depths, and under certain con- 

 ditions moderate currents may exist in the deepest 

 oceans. In a general way shallow waters are asso- 

 ciated with the stronger currents, the coarser deposits, 

 varied conditions of temperature and accessibility to 

 solar light. Deposits of extreme fineness may occur 

 in shallow and cold seas, which conditions would be 



nearly the same as those of the deepest seas ; for, 

 irrespective of depth, the principal difference is pre- 

 sence of light in the shallow water. This would 

 allow of the existence of species to which ordinary 

 light is directly or indirectly essential, along with such 

 of the deep-sea forms as could live in association with 

 them. In the shallowest waters along the sea margin 

 we find a certain relation between the depth and 

 particular groups of species of organisms ; but ex- 

 amination shows that this relation holds because 

 certain conditions of temperature, exposure to air, 

 food, &c, concur with such depths. These condi- 

 tions may correspond with a certain depth in one 

 area and with a different depth in another area ; so 

 that it becomes necessary to take many circumstances 

 into account before drawing conclusions as to depth 

 from the association of certain species. When the 

 conditions regulating the co-existence of particular 

 species are known, we can readily infer somewhat as 

 to the depth of the water. These considerations have 

 an important bearing upon the geographical distri- 

 bution of species and the inferences deducible from 

 such distribution in space and in time, and, conse- 

 quently, upon the continuity of oceans in space and 

 in time, or, rather, on the continuity of certain oceanic 

 conditions. A. Ramsay. 



( To be continued. ) 



BOTANICAL WORK FOR APRIL. 



THE early part of the present month will be the 

 season to work at several species : thus, the 

 common Pilewort [Ranunculus Ficaria, L.) is now 

 in full bloom in some parts of Britain. We have 

 been recently taught to regard it as comprehending 

 two distinct species ; for example, it is divided 

 into two varieties, viz., a. diverge/is, F. Sch. ; 

 b. inatmbens, F. Sch. The first variety, a, has lobes 

 of lowest leaves not oz'crlapping at the base, lowest 

 sheaths narrow : variety b, incumbens, has lobes of 

 lowest leaves overlapping at the base, or parallel with 

 petiole and lowest sheaths, very broad, amplexicaul. 



Which of these varieties occurs in your district ? 

 It will make many a walk pleasant and delightful to 

 know one is helping to clear up a question not yet 

 satisfactorily answered. 



In the south of Europe another form is found ; in 

 fact, a distinct species, named by most botanists 

 Ranunculus Ficariaformis. Have we not overlooked 

 it in England? It is very similar to our plant, and 

 may quite possibly have been passed over. Let it lie 

 cleared up this spring. 



Viola sylvatka, Fries. — This is another species 

 which can be worked up in April. Most of our 

 readers are aware that from the days of Linnceus 

 until a very few years ago, this plant passed current 

 under the old name of V. canina; nay, not a few still 

 persist in knowing it under the old name, and refuse 

 to listen to the '"new species." Linnceus's name 



