504 



Notices of Memoirs — 



noted). The fragments in the crucible are then taken one by one 

 and carefully placed in the burette, care being taken at the same 

 time that nothing is lost in the transference. The finer debris may 

 be left in the crucible. During the transference the burette may 

 be smartly tapped from time to time to detach air bubbles from the 

 fragments. The crucible is again weighed — say the weight is 

 now W. The height of the water in the burette is now taken. 

 Say it is X' c.c. When we have W — W = weight of substance 

 taken, X — X.' = number of c.c. occupied by quantity of substance 

 taken, whence _^~^, = specific gravity required. 



I append the first ten determinations which were made by this 

 method. Some of them were checked by other methods. From 

 these the general accuracy of the method will readily be inferred. 



Quantity 

 Rocks, Minerals, Sands, etc. taken. 



Grams. 



Granite 10-822 



Porph}Titic Olivine Basalt 8"483 



Fine Sandstone 11-47 



Sandstone cemented with Ba SO^ ^ 14-062 

 „ CaFoi ... 13-447 



Calcite 10-17 



Basic Eock (altered) 13-452 



Garnet and Iron Sand 14-88 



Same by Sp.g. bottle ... 6-813 



Shot in large pellets 79-328 



(again) 103-754 



Epidiorite 13-953 



By Sp.g. bottle 4-84 



No. of c.c. 

 displaced. 



4-1 



2-9 



4-4 



4-4 



4-85 



3-7 



4-9 



3-8 



7-1 

 9-3 

 4-9 



Calculated 

 Specific Gravity. 



2-64 



2-925 



2-6 



3-2 nearly 



2-77 



2-75 nearly 



2-74 



3-92 ) 



3-936 j 

 11-17) 

 11-16 j 



2-85 \ 



2-84) 



nisTOTioiBS o:f :]vn:EnvnoiK,s, ieto. 



I. — Floras of the Past : their Cobiposition and Distribution.^ 

 By A. C. Seward, F.E.S., Fellow and Tutor of Emmanuel 

 College, Lecturer on Botany in the University of Cambridge. 



AFTER speaking of the important work accomplished by 

 Professor Williamson, of Manchester, as a palseobotanist, and 

 referring to his methods of microscopic investigation of the Car- 

 boniferous plants, Professor Seward said : — My aim is to put 

 before you in this address one aspect of palasobotany which has 

 not received its due share of attention : I mean the geographical 

 distribution of the floras of the past. I recognise the futility of 

 expecting conclusions of fundamental importance from such an 

 incomplete examination of the available evidence as I have been 

 able to undertake ; but a hasty sketch may serve to indicate the 

 impressions likely to be conveyed by a more elaborate picture. 



1 Brit. Assoc. Eep. 1901, p. 649. 



2 Being the Presidential Address to the Botanical Section of the British Association 

 for the Advancement of Science, Southport, September, 1903. 



