Green’s Dictionary of Slang

unrestrained, noisy activities; occas. in sing.

1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 85: Running up and down, as in a fair, rolling among the hay, or flaunting at Vauxhall; these are gammocks truly.
1827		Examiner 19 Aug. 5/2: The gammocks of this set of indiscriminating monument destroyers [...] form not the most pleasing of all incentives to laughter.
1849		Hants Advertiser 20 Jan. 6/2: I sees many of their [i.e. tramps’] gammocks; when they goes up to the door they begins shivering [...] as if they was poorly or starved.
1865		Islington Gaz. 20 May 2/2: If suck ‘gammocks’ were attempted in Cheapside [...] they would very speedily be stopped.
1878		‘’Arry to the Front!’ in Punch 9 Mar. 100/2: The Nobs, as a general rule, / Are down on us Commoners’ gammocks.
1887		‘’Arry on Angling’ in Punch 30 July 45/1: Though I must say I missed the Thames gammocks, the snide comic song, and the shout.
1891		‘’Arry on Wheels’ in Punch 7 May 217/2: A rush twelve abreast is a gammock, twelve squeakers a going like one.