Just as the $1 and $2 definitive postage stamps issued in March 1972 remind us of our urban centres, Canada's new medium value denomination remind us of the tremendous variety in our nation's terrain. The immensity and diversity of Canada are almost incomprehensible; few other nations have the challenge of the seas, the woodlands, the prairies, the mountains and the north. Our country, a land of breathtaking beauty, has inspired Reinhard Derreth, of Vancouver, to create these designs which capture something of the vastness and beauty. Canada's western mountain areas, inhabited by mountain sheep and other magnificent species, are represented on the 15c. denomination. From spring to fall, the sure-footed bighorn wanders among the crags and rocky ledges searching for grasses. With the advent of cold weather, the rams and ewes form a single band and move to lower altitudes for mating. The offspring are born in late spring. Dark in colour except for lighter rump and under areas, the mountain sheep has horns which are dark and curved in a half-circle.