190 Mr Brooke’s Remarks on Dr Brewster's Reply 
struction has no resemblance to that of macled or hemitrope crys- 
tals for the four rectangles are portions of one crystal f which is 
very evident, supposing the figure to be correct. But it is said 
in p. 5, “ The interior conformation of apophyllite [tesselite] 
presents us with the new fact in crystallography, that a regular 
crystalline form arises in some cases from the union of smaller 
crystals, whose homologous sides are not parallel to each other . ” 
The four rectangles are portions of one crystal in the first para- 
graph, and in the second they are smaller crystals , whose homo- 
logous sides are not parallel to each other. How are those opi- 
nions to be reconciled P But it is unnecessary to discuss this 
point, as Dr Brewster has, in a memoir inserted in the Edin- 
burgh Philosophical Transactions for 1823, virtually abandoned 
this early view of the rectangular structure of the crystals of 
tesselite , and has substituted for it a new theory of their forma- 
tion, not less extraordinary than the phenomena from which it 
has been inferred *. Dr Brewster there says, that the tesselite 
coidd not have been formed by the ordinary process of crystallisa- 
tion, but that <£ a foundation appeals to be first laid by means 
of uniform homogeneous plates , the primitive form of which is 
pyramidal ; a central pillar, whose section is a rectangular lo- 
zenge , then rises perpendicularly from the base , and consists of 
similar particles . Round this pillar are placed new materials , 
in the form of four trapezoidal solids , the primitive form of 
whose particles is prismatic , and in those solids the lines of simi- 
lar properties are at right angles to each other. The crystal is 
then made quadrangular by the application of four triangular 
prisms of unusual acuteness. These nine solids , arranged in 
this symmetrical manner , and joined by transparent lines per- 
forming the functions of a cement , are then surrounded by a 
wall composed of numerous films , deposited in succession , and 
the whole of this singular assemblage is finally roofed in by a 
plate exactly similar to that which formed its foundation ! n 
Ample as the preceding remarkable description may appear, 
it is yet deficient in several important particulars. What is the 
figure of the solid which Dr Brewster calls the primitive form 
* This memoir is said to have been read in 1817 and 1821. How has it hap- 
pened that Dr B. should have suffered so curious a discovery to sleep so many 
years in the archives of the Society ? 
