1871.] 



HEEMAN AILOPHANE. 



235 



Northampton. 



, " ~s Charlton. 



I. II. Mean. 



Water expelled at 100° C. 24-70 24-88 2480 27-11 



„ fixed at 100° C. 14-54 14-54 14-64 15-80 



SiO„ 23-09 22-92 2301 20-50 



AI2O3 31-24 31-42 31-33 31-34 



Fe^Og 2-35 2-18 2-26 



FeO -31 



CaO 2-51 2-48 2-49 1-92 



MgO -01 -01 -01 



(Normal) CO^ 1-28 1-28 128 1-69 



(As bicarbonate) COj 104 



99-72 99-71 99-72 99-71 " 



In these analyses tlie amount of carbonic acid was deducted from 

 the loss on ignition ; and in Mr. Northeote's case, in addition, the 

 carbonic acid existing as bicarbonate was deducted from the loss at 

 100° C. 



The excess of silica in the Northampton specimen is probably due 

 to an almost unavoidable admixture of sandstone, upon which the 

 allophane formed an incrustation. 



Mr. Sharp, in a paper lately read before the Geological Society of 

 London, and published in the Quarterly Journal of the Society, 

 vol. xxvi. p. 367, speaking of a section of the Northampton Sand in 

 the grounds of the Northampton Lunatic Asylum, remarks : — 



" One set of joints in this section have a direction N.W. and S.E. ; 

 and the crevices are frequently filled with a soft white material, 

 which, upon analysis by the recently deceased Dr. Berrill (formerly 

 a student at the Royal School of Mines), was shown to be allied to 

 allophane." 



The substance here alluded to, a dull, whitish, pulverulent, earthy 

 mineral, that may be polished by the nail, adhering strongly to the 

 tongue, and exhibiting no trace of crystalline structure under the 

 microscope, is by no means rare in many localities both in the iron- 

 stones and limestones of the Inferior Oohte of the Midland Counties, 

 Professor Morris, in his paper on the allophane of Charlton*, 

 apparently alludes to a similar mineral. He says : — During the im- 

 portant investigations (under the direction of Dr. Percy, at the School 

 of Mines) into the chemical composition of the different iron-ores of 

 Britain, a white powder (probably pholerite) was observed associated 

 with some of the clay-ironstone ; the following is its analysis by Mr. 

 Dick :— 



SiO„ 41-78 



ALO3 36-99 



HO 14-26 



Fe„03 4-51 



CaO -48 



MgO -16 



Alkalies undetermined . 



98-18 



* Quart. Journ. Geol. Soc. vol. xiii. (1857) p. 15. 



