Pembina Region of North Dakota— Berkey. 1 5 1 
other. A partial analysis for comparative purposes on two 
typical samples sent from these localities gave: 
Tongue river sample — Residue 27.9 per cent; CaCO' 55.13 per cent. 
Pembina river sample — " 29.4 " " 53.20 " 
In each case the sample is not the maximum limit for 
lime content. Another sample of the Pembina locality 
marls gave : 
Insoluble residue 14 . 00 per cent. 
Iron and alumina 18.00 per cent. 
Carbonate of lime 60 . 00 per cent. 
Moisture 8 . 00 per cent. 
Clay Shales. — Below the cement marls, in the Pembina 
section, lie a thick series of clay shale beds. They are lam- 
inated more prominently than the marls, and are very plastic 
on weathered outcrops. Their chemical constituents lime and 
iron, vary widely in different beds. This is the lowest forma- 
tion exposed anywhere in the "Pembina mountain" region. 
Most of the rivers have not eroded deeply enough to reach 
it. 
Partial analysis of two samples of these shales at differ- 
ent horizons gives the following percentages : 
No. 0. " No. 4. 
Silica — SiO' 61.03 per cent .61.52 per cent. 
Alumina — APO^ 22 . 70 per cent 18 . 65 per cent. 
Iron — Fe^O^ 6 . 53 per cent 4.90 per cent. 
Lime — CaO 97 per cent 75 per cent. 
Magnesia — MgO 51 per cent 1.32 per cent. 
Water— H-0 7.92 per cent 8.80 per cent. 
99.66 per cent. 95.94 per cent. 
In the above all the iron was measured as Fe^O^, al- 
though it is not all in that form, the column for water also 
includes other easily volatile constituents, and no effort was 
made to measure the alkalies. The analysis serve however 
to determine the general range of composition. 
A systematic and thorough series of experimental tests 
have been made on these clay shales to determine their value 
in brick and tile manufacture. Most of them have been car- 
ried out by the writer on a laboratory scale first and then, 
following the lines thus indicated for a particular horizon 
or bed, the appropriate practical test was made by taking a 
suitable quantity to an operating plant willing to run the 
