and the formation of Gypsum and Magnesian Rocks, 369 
Magnesian limestones often contain large admixtures of clay 
and sand; dolomite is not unfrequently the cement of breccias 
or conglomerates, as in the well-known conglomerate of the Per- 
mian system in England. Concretionary masses of dolomite 
sometimes occur in these aggregates, and in the Permian rocks 
of the Vosges are pr in’ bed of a sandy clay, itself occasion- 
ally cemented by nto 
I have irri fe ‘deweribed two remarkable ones con- 
ie: of 
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stratified with this last are beds of bituminous igellweW ebtlste 
ing sia vp containing carbonate of iron, and always intermixed 
with more or less sand or clay or both; the clay in one speci- 
men dincentsh to fifty per cent, while another quartzose variety 
gave carbonate of lime 58°04, carbonate of magnesia 31°96, car- 
nate of iron 5:80, silicious sand 880=99-60, The latter is a 
friable crystalline rock, showing in its fracture broad surfaces of 
Cleavage, like the crystals of Fontainebleau sandstone. ese 
dolomites, which contain no fossils, are occasionally traversed ao 
Veins of quartz and peers a spar, or contain small masses of 
pein of the travertine. 
_ The conglomerates of this series inclose in a paste of ferrifer- 
ous dolomite, grains and rounded fragments of limestone, often 
having the characters of the associated travertine, together with 
sm asses 
ents of quartz and mi oe an a nearly 
Hee yellowish crystalline dolomite; these are ah baa 
onary in their origin and noti mbedded saeetea! ae 
The other conglomerate to be ae occurs on 5 tha islands of 
Montreal, Se — and several other localities in the neigh- 
borhood, an d belongs to to small detached patches of the Lower 
Sot series, left after denudation, which Tepose ee 
n 
sat sermac~ Vor. XXVIII, No. “a1. —NOV., 1 
7 
