4 The Rev. P. Keith on the Structure of Animals, 



that the prismatic form of the witherite has modified it so 

 as to produce a species of hybrid or intermediate form, hav- 

 ing the prismatic character with a less degree of obliquity 

 (102° 54'') than the rhomboid, then it would be unnecessary as 

 yet to consider either the witherite as di-, or the carbonate of 

 lime as ^n-morphous. How far such a combination of the 

 forms is possible, I am not prepared at present to investigate ; 

 it will probably, however, be from the study of the forms of 

 compound minerals, resulting from the union of simple minerals 

 whose forms are known, that we shall arrive at the first general 

 conclusions in regard to the connexion of the forms of che- 

 mical compounds with those of the elements of which they 

 consist. 



It is not unworthy of remark, that the right rhombic baryto- 

 calcite is harder and heavier than the oblique, a relation 

 similar to that which arragonite bears to the rhomboid of car- 

 bonate of lime. If we take the mean specific gravity of calc 

 spar at 2*65, and that of the witherite at 4*3, and multiply 

 each by their atomic weights, and divide the sum of the pro- 

 ducts by the sum of the weights, we obtain for the specific 

 gravity of a compound of the two, atom to atom, 3'707j rather 

 less than the mineral was found to possess by experiment. 



In a letter I have just received from Professor Torrey of 

 New York, he mentions a mineral under the name of baryto- 

 strontianite, found in considerable quantity at Kingston, Upper 

 Canada. It is not unlikely that an examination of the forms 

 of this compound mineral might lead to interesting results. 

 Unfortunately, the specimens he sent with the letter have mis- 

 carried. Should this meet his eye, he may, perhaps, find an 

 opportunity of transmitting others. 



Durham, November 1834. 



II. Of the Structure of Animals, By the Rev. Patrick Keith, 



F,L.S. S^c,"^ 

 npHE writer who undertakes to describe the productions of 

 -■- animated nature, whether botanical or zoological, soon 

 finds out the impossibility of examining each individual singly. 

 It would be a labour altogether interminable. But the means 

 of abridging it readily suggests itself; it is that of combining 

 into distinct groups or families all such individuals as are 

 found to exhibit a close resemblance in external form, or in 

 internal constitution, and of designating them under a com- 

 mon appellation. We are led irresistibly to regard them as 

 allied together by nature, and possessed of kindred qualities. 



• Read before the Hythe Reading Society March 7, 1833; and commu- 

 nicated by the Author. 



