LIMESTONES OF SOUTH DEVON. 385 



Xo. 3. Chiefly made up of micro-crystals of quartz, containing 

 liquid inclusions, and of flakes of mica. 



(d) Barton Limestone Residues. — l^o. 1. The very fine portion is a 

 siliceous paste similar to that described as occurring in previous 

 residues. 



The heavier portion includes (1) micro-crystals of quartz, most of 

 which contain inclusions, and to such an extent do these inclusions 

 occur that masses of them resemble nuclei ; (2) flakes and small 

 masses of siliceous material which are important as throwing light 

 on the origin of the micro-crystals of quartz referred to in de- 

 scribing this and previous residues. This siliceous material is 

 crowded with liquid inclusions (PI. IX. figs. 1 & 2) and around the 

 edges passes into the crystalline condition, portions of which become 

 detached and then appear as aggregates of, or single micro- 

 crystals of quartz, the origin of which is thereby explained. 



Xo. 2. In this we get a quantity of siliceous an„ micaceous 

 material, some fragments of which are remarkable for the great 

 number of microlitic needles which occur in them, llicro-crystals 

 of quartz are also present, and contain the usual inclusions. 



Xo. 3. The residue is entirely made up of micro-crystals of 

 quartz containing inclusions. As these are the most perfect that I 

 have obtained, I have represented them in PI. IX. fig. 5. They vary 

 in length from O'l to 0"5 mm., and their form is the typical prism 

 with pyramidal terminations. 



(e) Bunscombe Limestone Residues. — These are from the same 

 quarry as the specimens from T^'hich the thin sections were taken 

 (see J). 379). 



Xo. 1. A siliceous paste, crowded with microlitic needles and 

 microlites. 



Xo. 2. The portion of least specific gravity is a micaceous 

 siliceous paste, crowded with microlitic needles and microlites. 



The heavier portion includes siliceous and micaceous flakes, some 

 of which are crowded with microlitic needles. 



Xo. 3. From the Goniatite Limestone. This is similar to Xo. 1, 

 the only difference being that microlitic needles are more numerous, 

 and there are siliceous flakes so crowded with these needles as to be 

 much darkened. 



It may be well to again emphasize the fact that the Goniatite 

 Limestone contains 10*2 per cent, of residue as compared with 1*8 

 per cent, in the limestones below it. The residual constituents are 

 similar, but the great difference in the quantity points to a dissimi- 

 larity in the conditions under which the two limestones were 

 deposited. 



§ 6. Conclusions deawn prom examination op the Eesidtjes. 

 The variety of mineral constituents in the residues is small, and 

 has therefore necessitated considerable repetition in the descrip- 

 tions, but the conditions of preservation differ. Of the detrital 

 elements it is difficult to speak ; it is indeed doubtful which minerals 

 are of detrital origin. In residues which I have obtained from 



