Coal was and still is, literally, the driving force in America. Practically nothing ran without it back when these cards were produced. Coal is still the largest energy source in the country with 50% of the power produced is with coal. To illustrate this, in 1915, there were 140 coal dealers. Check your phone book and see how many you can find. Although coal is still extremely important in today's society I only found one. Mergers have formed mega Corporations.
Trum Coal
Co.
Superior
Fuel
Island Creek Coal
Steamer Catharine Davis

Blue Pennant Coal
Yellow Jacket Coal
Both of the above cards were sent out by The Middle West Coal Co., Inc. You would think these two cards were of the same era but check the backs and you will see they were mailed 12 years apart. Their offices were in the 1st National Bank Building. The same Building where the Marmet-Halm Coal Co. were located. Not to mention The Diamond Coal & Coke Co., The Chesapeake & Ohio Coal & Coke Co., Belmont Coal, Raleigh Coal & Coke Co., Raymond City Coal & Coke co., The E. L. Sternberger Coal Co., The Waldensia Coal & Coke Co., The Winifrede Coal Co. I would think that this building was probably kept pretty warm during the winter months.

Blue Diamond Coal Co.
Adam F. Meyer Coal Co.
Cincinnati and North Bend Offices and facilities of the Marmet-Halm Coal & Coke Co. Their mines were in West Virginia.

These are on the backs of all these cards
In the first card in the middle row above you can see Covington KY. as seen from Marmet Coal Yards with the coal boat Florence Marmet in the lower left. The next card is a real photo postcard of the boat. The 3rd & 4th cards show the coal boat Otto Marmet being built. You can see the Florence Marmet in the flood & ice gorge part of the disaster section.
These are not postcards

1912 Marmet ad
1894 Ad.

Both sides of a double card for Grenadier "Rainbow" Stoker Coal