Armstrong’s most prolific works are the cover designs for the Henry Van Dyke series that span the years of 1895 to 1926. The most notable of these are covers printed on dark blue cloth that feature gold highly ornamental and symmetrical designs in gold and other brightly contrasting inks.
Little Rivers, 1895
Fisherman’s Luck, 1899
The Ruling Passion, 1901
The Blue Flower, 1902
Days Off, 1907
Out-of-Doors in the Holy Land, 1908
The Unknown Quantity, 1912
The Valley of Vision, 1919
Camp-Fires and Guide-Posts, 1921
Companionable Books, 1922
The Golden Key, 1926