The subconscient is a dark and ignorant region, so that it is natural that the obscurer movements of the Nature should have more power there. It is so indeed with all the lower parts of the nature from the lower vital downwards. But it does send up good things also though more rarely. It has in the course of the sadhana to be illumined and made a support of the higher consciousness in the physical nature instead of a basis of the instinctive lower movements. page 1592 - 93 , Letters on Yoga , Volume 24 , SABCL

It is only if the mind is silent that the subconscient can be empty. What has to be done is to get all the old ignorant un yogic stuff out of the subconscient. page 1594 , Letters on Yoga , Volume 24 , SABCL