sas to R

This could be similar to a multi-location RCB design were "trial" is
location.  Since no distribution is specified, the distribution is
assumed to be Gaussian.  Make sure that trial, block, trt are factors,
this should be similar to SAS:

lmer(y ~ trt + (1|trial/block/trt), data=df)

proc glimmix data=df;
class trial block trt;
model y=trt;
random trial block(trial) trt(block*trial);

Kevin Wright