HARDWICKE'S SCIENCE-GOSSIP. 



C? 



docs uot usually complete its flowering until May, 

 in which case the flowers are usually, though not 

 always, more perfect. The legends about this tree 

 in the West are still believed by many. It is 

 asserted that it was derived from Joseph of Arima- 

 thea's staff, which, by the way, was a blackthorn- 

 one of course planted with the small end in the 

 ground. Well, it grew up a whitethorn, and doubt- 

 less a mere variety of the Cratagus oxyacantha. Of 

 course all this was miraculous ; and to this day this 

 thorn is looked upon by many " wold folk " as an 

 astounding miracle, as it is confidently averred that 

 its constant flowering on or about old Christmas- 

 day is an evidence that ibis is the right day, and as 

 such it is still kept by some. I have met with a 

 similar variety in a hedgerow at Alfrick, in Wor- 

 cestershire, and very early May -trees are not 

 uncommon in parts not connected with Glaston- 

 bury, and indeed where quite a different climate 

 prevails. These seem to be merely varieties which 

 correspond to the early and late sorts of different 

 fruits and vegetables.— Jamss Buckmcui, Bradford 

 Abbas. 



GEOLOGY. 



The Origin and Mechanise of Production 



OF THE COLUMNAR STRUCTURE OF BASALT.— This 



is the title of a paper just read to the Royal Society, 

 by Robert Mallet, C.E., P.R.S. The author shows 

 that all the salient phenomena of prismatic basalt as 

 observed in nature can be accounted for as results 

 of contraction by cooling in a homogeneous body 

 possessing the properties of basalt, and that the 

 theories hitherto advanced and repeated in text- 

 books of the production of basaltic prisms are alike 

 untenable and unnecessary. If a large level and 

 tabular mass of homogeneous basalt cool slowly by 

 loss of heat from one or more of its surfaces, tbe 

 contraction of the mass while plastic will be met by 

 internal movements of its particles ; but when the 

 temperature has fallen to a certain point of rigidity, 

 reached at between 900° and 000° P., splitting up 

 commences, and that surface will begin to divide 

 itself into similar geometric figures of equal area, 

 which on mechanical principles must be hexagons, 

 the diameter of which is shown to depend upon the 

 relation that subsists between the co-efficients of ex- 

 tensibility of the material and of its contraction by 

 cooling down to the splitting temperature. These 

 hexagons are the first-formed ends of the future 

 prisms, which split deeper into the mass as cooling 

 down to the splitting temperature reaches deeper 

 into it. When the prisms have split down to a 

 certain distance, further cooling proceeds, not only 

 from the ends of the prisms, which formed the sur- 

 face of original cooling, bnt from the sides of the 



prisms. Now, as each prism is coldest at the end, 

 and hottest where in the act of splitting, and is also 

 hotter along the axis than at the exterior of each 

 prism, so, by contraction, differential strains are pro- 

 duced in each prism, both parallel to the axis and 

 transverse to it, which result in cross fractures at 

 intervals along the length of thepiism, the distances 

 between which the author has assigned. Transverse 

 fracture round the prism must commence in the 

 outer couche in a plane normal to the resultant of the 

 contractile strains longitudinal to and transverse to 

 the axis of the prism ; the fracture commences, 

 therefore, oblique to the prismatic axis. This obli- 

 quity diminishes as the transverse contractile force 

 diminishes, as the conferential couche of cooling 

 reaches nearer to the axis of the prism ; the result 

 is that the transverse fracture when completed is 

 lenticular or cup-shaped, the convex surface always 

 pointing in the same direction in which the cooling 

 is progressing within the mass. If the mass cool 

 from the top surface only, the convex surfaces of the 

 cup-shaped joints will all point downwards; if 

 cooled from the bottom only, they will point 

 upwards; and if from both surfaces, the convexity 

 of the joints will be found pointing both upwards 

 and downwards in the mass. As the splitting 

 always takes place normal to the surface of cooling, 

 so, if that surface be level and cool uniformly, the 

 prisms must be vertical and straight ; also, if the 

 cooling surface be a vertical or inclined one, the 

 direction of the prisms will be normal thereto. If, 

 however, the mass cool from its upper or lower sur- 

 face, but of much greater thickness in one direction 

 than in the opposite one, the prisms formed will not 

 be straight, but have their axes curved, because the 

 successive couches reaching the splitting temperature 

 successively within the mass, and normal to which 

 the splitting takes place, are themselves curved 

 planes. These are a few of the principal points of 

 this paper, which the author believes renders, for 

 the first time, a complete and consistent account of 

 all the phenomena observed in prismatic basalt. A 

 considerable number of these phenomena were re- 

 ferred to and explained by the author. At the con- 

 clusion of his paper Mr. Mallet submits to rigid ex- 

 amination the notions which from 1S01, the period 

 of Mr. Gregory Watt's paper {Phil. Trans.) to the 

 present time, have continued to occupy the text- 

 books of geologists, and he points out how entirely 

 these fail to account for phenomena. 



The Structure and Age of Arthur's Seat, 

 Edinburgh.— Mr. John W. Judd, P.G.S., in a 

 paper just read, says that Arthur's Seat, so long the 

 battle-ground of rival theorists, furnished in the 

 hands of Charles Maclaren a beautiful illustra- 

 tion of the identity between the agencies at work 

 during past geological periods, and those in opera- 

 tion at the present day. One portion, however, of 



