138 



KNO WLE DGE 



[July 1, 1893. 



that it is not a sed:"mcntary rock. The total absence of 

 organic remains tends to tlie same conclusion. There is, 

 in fact, a lack of all positive evidence for a sedimentary 

 origin of these beds. 



Gypsum and dolomite occur in the red marl in a remark- 

 able manner, which receives from Mr. Middlemiss an 

 ingenious explanation in accordance with his view as to 

 the origin of the formation. The gypsum occurs as a net- 

 work, or sponge-work of anastomosing strings ; the 

 dolomite in vesicular or honey-combed lumps of irregular 

 shape and size. Besides these, there occur in the marl 

 numerous pale greenish-grey patches, varying in size from 

 an inch across to mere specks. Every gradation may be 

 traced from these to the honey-combed dolomite. As tlie 

 latter become more honey-combed, they split up into 

 corroded fragments of dolomite, and these latter, again, 

 into the greenish grey specks and patches. They become, 

 in fact, a part of the marl. As Mr. Middlemiss remarks, 

 the red marl "seems to have devoured the dolomite, to have 

 absorbed or digested it just as a pot of molten lead absorbs 

 the solid bits thrown into it." 



A parallel change from dolomite to gypsum also occurs. 

 Roughly-beJded dolomite, solid in iis central portion, is 

 found to be crumbling and honey-combed at the edges. 

 The following series of changes occur : — 



First, the hard, tlinty-looking rock becomes dotted with 

 minute punctures in rows or nebulous patches. Then 

 larger ragged holes appear, themselves bordered by minute 

 punctures. Canals, sometimes roughly following the joint 

 planes of the dolomite, join these larger holes. Another 

 phase in the gradual change is dolomite with a honey- 

 combed structure. The joint planes are converted mto 

 widened fissures, and along the cracks and holes gypsum 

 takes the place of the dolomite. Finally lumps of dolomite 

 are honey-combed to a spongy, and then to a reticulate 

 fibrous texture, the holes and meshes being occupied by 

 gypsum. 



The general position and stratigraphical relations of the 

 salt marl furnish further arguments against its sedimen- 

 tary origin. Above the red marl lies the purple sandstone, 

 and it has been held that there is a normal passage of the 

 red marl into the purple sandstone, such as to indicate a 

 continuous sequence between the two formations. Mr. 

 Middlemiss contends that there is not such a normal 

 passage. Continuous seijuence, he asserts, is best shown 

 by the intcrhiddiiiii of the one formation with the other ; 

 alternating layers of the one and the other dovetailing the 

 two formations together. This is not found ; nor could 

 Mr. Middlemiss satisfy himself that tliere is any rock 

 intermediate in composition between the marl and the 

 sandstone between them. In exposed sections showing 

 the junction, it is pointed out that the layer of rock 

 marking the junction is brecciated. In one section the 

 junction-marking breccia of fragments of purple sandstone 

 in a matrix of marl is explained by Mr. Middlemiss as 

 possessing the appearance of one formed by tlic liitnision of 

 (Hie roc); into tinotlicr. 



Other sections are brought forward to show that the 

 red marl must have possessed a plasticity and power of 

 movement after the deposition of many of the formations 

 above it. Where the marl is overlaid by a boulder bed, 

 the latter never contains fragments or boulders of marl. 

 At the sume time tlie boulder bed does contain fragments 

 of dolomite similar to the unaltered portion of the dolomite 

 of the red marl. From this Mr. Middlemiss infers that 

 the dolomite of the red marl represents an original rock at 

 least older than the boulder bed; while the red marl, 

 gypsum, and altered dolomite are of more recent age. 

 And in a section where the marl occupies the core of a 



sigma-flexure, while the other formations included in the 

 flexure are sheared, the marl is not. The conclusion from 

 such a section seems to be that the marl band had been 

 forced in a plastic or liquid condition among the other 

 rocks, and had solidified under conditions of no strain. In 

 another section the red marl exhibits one of the distin- 

 guishing characters of intrusive rocks ; it alters its horizon 

 with regard to the accompanying sedimentary beds — that 

 is to say, from a position in one place below the speckled 

 sandstone, it passes to one above it. In other places the 

 salt marl is overlaid by the orange series (younger tertiary), 

 and it is concluded that the junction cannot be a normal 

 one due to the deposition of these beds on an exposed reef 

 of salt marl. 



To account for all the above remarkable, and on the 

 sedimentary theory anomalous, features of the red marl of 

 the Salt Range, Mr. ]\Iiddlemiss suggests a remarkable 

 hypothesis of arrested volcanic action. The striking absence 

 of all outward tokens of volcanic activity, metamorphism 

 and disturbance generally, in the region under consideration 

 is pointed out. Thus it would appear that the sub- 

 terranean magmas have remained sealed up since the 

 earliest era of sedimentation ; but the upper surface of 

 the molten mass would solidify, and it is suggested that 

 the scum thus formed is represented by the salt marl. 

 The dolomitic masses are accounted for by the alteration 

 produced on overlying dolomitic rocks by this subterranean 

 mass. 



In the second paper, Mr. Holland furnishes some inter- 

 esting notes on the chemical and physical characters of 

 rock specimens from the Salt Range, and in a certain 

 degree confirms the hypothesis suggested by Mr. Middle- 

 miss. We have first an examination of the bi-pyramidal 

 quartz crystals, the " Marf diamonds " of the natives. 

 These crystals are found embedded in the gypsum, and 

 vary in size from a millet seed to that of a walnut. In 

 colour they vary from white through shades of pink to 

 brick red, and in the centre of each crystal there is a 

 white or pink translucent core. The perfection of the 

 crystals, and the absence of all traces of rounding, is held 

 to be rather characteristic of their formation in a yielding 

 liquid magma than Ln an ordinary sedimentary formation. 

 Microscopical examination and analysis showed that these 

 translucent cores are due to inclusions of anhydrite. 

 The conclusion to be derived from this seems to be that 

 the quartz crystals were formed in the midst of a matrix 

 of anhydrite, and that afterwards the anhydrite was 

 hydi-ated to gypsum ; and a study of the gypsum itself 

 shows clearly that it has been formed by the action of 

 water on anhydrite. Specimens examined were found to 

 be partly anhydrite and partly gypsum. In some the 

 alteration to gypsum occurred along cracks and cleavage 

 planes. The expansion which accompanies this change 

 has left its mark, and displacements of fragments, faulting 

 of twinning and cleavage planes, are observable under the 

 microscope. In some cases the crystals have been frac- 

 tured, and the fragments scattered along lines so as to 

 produce a fohated structure, sometimes observable in hand 

 specimens. 



Mr. Holland concludes from his studies that the gypsum 

 masses are not of aqueous or sedimentary origin. He 

 suggests further that the anhydrite may have been pro- 

 duced by the action of sulphuric acid on limestone at high 

 temperatures, and with presence of superheated waters. 



As to Mr. Middlemiss's hypothesis of arrested volcanic 

 action opinions may difi'er, but it must be admitted tiiat 

 these two papers render extremely probable the conclusion 

 that the red marl of the Salt Range is not an ordinary 

 sedimentary rock. 



