Amitryptiline is a tricyclic antidepressant not a selective serotonin reuptake inhibitor.

to prevent or relieve depression

The S stands for serotonin and the N stands for norepinephrine and RI stands for reuptake inhibitor. So, obviously these drugs are supposed to work on both serotonin and norepinephrine. However, some literature uses SNRI to mean Selective Norepinephrine Reuptake Inhibitor, and this will work better on norepinephrine. Then you have the SSRI which is Selective Serotonin Reuptake Inhibitor, which works better on serotonin.

Zoloft is an antidepressant of the selective serotonin reuptake inhibitor class.

No, Zoloft is a selective serotonin reuptake inhibitor or SSRI.