SCIENCE- GOSSIP. 



307. 



Profcsior Ili'ljcrt in 1863, has bctn considcraMy ex- 

 tended |jy Dr. C. Harrois, and is being very widely 

 adi)pted. , 



The VVealden was at one time reganled as part of 

 the Jurassic or Oolitic system. It has since Iwen 

 separated from this association, and placed liclow the 

 base of the Cretaceous. In a similar manner the 

 I'urbccUs, at the top of the Jurassic, are more 

 correctly regarded, together with the Wealden, as 

 passage formations, containing as they do fossil 

 representatives both of Jurassic and Cretaceous times. 

 In Southern France, and on the south slopes of the 

 .Alps, there are rocks known as Tithonian, which are 

 regarded by Krench geologists as Cretaceous. I'ossi- 

 bly they are of preVVealilen age or even contemporar)' 

 with that formation. The Tithonian includes the 

 well-known Diphya Limestone with its distinguishing 

 fossil Dip/iya lertbraliih. 



Interesting as would be a consideration of the 

 wonderful fossil remains discovered in the I'urbecks 

 and Wealden Heds, we must not linger over them, 

 since we have now relegated them to a new system — 

 the Ncocomian— and cut them off from the Cretaceous. 

 Suffice it to say in regard to the I'urbecks that in a 

 layer a few inches in thickness have been discovered 

 the jaws of no less than twenty-five species of a low 

 type of marsupial mammals. In older formations 

 than this, only four have been found in the Stones- 

 field (Oolite) Beds, and four in beds of Upper Trias 

 age. In the Chalk beds not any remains of mammals 

 have been found, so we have here the remarkable 

 fact that between strata which must themselves have 

 taken inconceivable .tges to form, and which are 

 utterly barren of mammal remains, there is isolated 

 this thin Purbeck seam containing so large an assem- 

 blage of them. There they are, and there is the 

 proof that they existed ; but there must have been 

 many more. The very fact of their existence impels 

 us to believe this. \'et thousands of feet of sand and 

 chalk are absolutely .silent as to mammal life, and not 

 until the Chalk age is past and gone do we find the 

 order of mammals again exhibiting its remains in the 

 rocks. Irhoiiodon, P/agiaiilax, and Spalacolhcriiim 

 are the generic names of three Purbeck mammals. 

 What became of their descendants in the Wealden 

 age ? 



How did these small creatures fare when they had 

 to struggle for existence amidst the forests tenanted 

 by giant lizard-like monsters, and when extinction 

 may fairly have been expected to wait upon them ? 

 For answer the geological record is silent. It is 

 possible that the evolution of the Marsiipialia, which 

 has been so successfully carried through in .Australia, 

 took a yet earlier start in the British area, and, like a 

 race "born out of due time," they actually did 

 become extinct when in the Wealden age giant 

 reptiles held the sceptre of power, when the great 

 Igiiaiiodon, Afega/osaiinis, KigiiosaiiniSy and many 

 another, lorded it over other creatures inferior in size 

 and strength, wliicli went to make the fauna of 

 portions of l^nglund, Belgium, and France in these 



pre. Cretaceous times. He that as it may, the 

 Cretaceous era was to p:iss away before mammals 

 again showed themselves, and then not until the 

 Paris gypsum came to be laid down in Kocene limes 

 were their remains again entombed. 



/guanotUn U\U<:'[ Matucll) Kentish Rag, Maidstone. 

 2, Femur ; 3, tibia ; 7, radius ; 8, various vertebrae ; 10, clavicle. 



The Ciault clay, forming the base of the system 

 with which we are particularly concerned, is a forma- 

 tion that is found, in connection with what has been 

 called the Upper Greensand, to occur with remark- 

 able consistency immediately beneath the chalk in 

 the South-East of England. Wherever in the south 

 of Cambridgeshire the chalk terminates at the surface 

 there is always lO be found, cropping from beneath 

 it, either the Upper Greensand or the Gault. Except 

 In North Kent, the Gault outcrops all around the 

 Weald with the greatest regularity, and stretches 

 from its most westerly termination near Selbome, in 

 Hampshire, to the Kentish coast ; at Folkestone in the 

 case of its northern branch, and to the Sussex coast, 

 near Eastbourne, in the case of its southern branch. 



( To be continiitd. ) 



The Vf.rkes Observatory is evidently doing 

 good work, according to its first annual report. 

 Good measurements of difficult objects have tieen 

 effected. The heat received from the star Arcturus 

 is about equal to that from a candle six miles 

 distant. — /•'. C. Dennett. 



