ICE CREAM SODA

The 'ice cream soda' or float is a treat made, typically, by mixing ice cream with either a soft drink or flavored syrup and carbonated water, often with some special technique to encourage the partial slushing of the ice cream itself.
The ice cream soda originated in the United States in the late 19th century. There are several legends about the invention of the ice cream soda, but it was most likely invented by either Robert M. Green of Philadelphia or Fred Sanders of Detroit.
Green's account was published in "Soda Fountain" magazine in 1910. He operated a soda fountain at the Franklin Institute's semi-centennial celebration in Philadelphia in 1874. Another vendor had a fancier, bigger soda fountain, so Green wanted to create a new treat to attract customers. After some experimenting, he decided to combine ice cream and soda water. During the celebration, he sold vanilla ice cream with 16 different flavors of soda water. The new treat was a sensation, and soon other soda fountains began selling ice cream sodas.
Fred Sanders owned a successful confectionery, the Pavilion of Sweets, in Detroit. One night, some customers came in shortly before closing time and ordered sweet cream sodas. Since Sanders had run out of sweet cream, he quickly concocted a new treat by adding ice cream to soda water. Sanders opened his first Detroit store in 1875, a year after Green served ice cream sodas in Philadelphia.
Whoever invented the ice cream soda, it quickly became very popular, to such a degree that it was almost socially obligatory among teens, although many adults abhorred it. According to legend, it was banned, either entirely or on holy days, by some local governments, giving rise to the ice cream sundae. However, there is no concrete evidence to support this legend about the origin of the sundae.

A typical recipe:

:soft drink of choice

:1 scoop of ice cream

:glass which is wider at the top than bottom

Slide one scoop of ice cream into bottom of glass. add soft drink mix and stir around a bit

to make it frothy.

Add a second scoop of ice cream, then spray the soft drink down side of glass to encourage

foaminess, until full.

Serve 

(the more basic, modern version is to put a couple of scoops of ice cream in a glass which has a narrow bottom and wide top, add root beer, and voila: root beer float)
Floats are referred to as 'spiders' in Australia and New Zealand, and the equivalent of the popular American root beer float is the sasparilla spider.