Thanks for your query,based on the facts that you have posted it appears that you have dark,solid bump on your foreskin.
This could be either a calcified vein ( one of the tributaries of Dorsal vein of penis) or a sebaceous cyst
.However final diagnosis can be confirmed only on diesct inspection and palpation of the bump.
Please consult qualified General Surgeon
for clinical assessment and further treatment which will depend upon the final diagnosis.